EP0692072A1

EP0692072A1 - Pressure medium driven device performing linear motion

Info

Publication number: EP0692072A1
Application number: EP94909953A
Authority: EP
Inventors: Reijo Karppinen
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-03-25
Filing date: 1994-03-24
Publication date: 1996-01-17
Anticipated expiration: 2014-03-24
Also published as: JP3538426B2; FI931324A; FI96132B; FI931324A0; EP0692072B1; DE69420713D1; WO1994021915A1; FI96132C; JPH08508076A; DE69420713T2

Abstract

A pressure medium operated device generating to-an-fro motion to one or several pistons (14, 15) or a similar motion transmitting arm, comprised of a primary piston (3), to which motion is brought in transmitting pressure medium alternately to its both sides. The control valve (8, 9) of pressure medium moving the primary piston (3) is inside the said primary piston.

Description

PRESSURE MEDIUM DRIVEN DEVICE PERFORMING LINEAR MOTION.

The invention relates to a device operated by pressure medium and producing linear to-and-fro motion. The device is characterized by the construction of a primary piston with necessary valves gene¬ rating the to-and-fro motion.

Previously known motion generating devices, are a.o. hydraulic cylinders working by pressure medium and different types of per¬ cussion machines, in which the percussion piston gets its motive energy in different ways from pressure medium. In percussion machines self-acting valves are used for control of medium, where¬ at the percussion machines perform, automatically, continuous to- and-fro motion. E.g. US patent 4,031,812. Generally, hydraulic cylinders are controlled by means of outside valves. In percussion machines a hydraylic accumulator, e.g. a blast tank, is used to charge sufficient pressure and discharge it instantly against a piston that is to be moved, in order to produce at least a one-way rapid piston motion. Generally, the valve actuators are in the body of the device and the piston is a component to transfer motion or power only.

Present devices are not applicable as permanently working gene¬ rators of to-and-fro motion only by hydraulic pressure, especially when the motion should be rapid in both directions, generation of pressure shocks in the valves avoided and one would not want to use a gas containing hydraulic accumulator in order to accelerate the motions.

With a device according to this invention, working by pressure medium, particularly fluid medium, a decisive improvment of this disadvantage is achieved and the invention is characterized in what is presented in the enclosed patent claims.

A most important advantage of the invention is that by means of a built-in valve reversal free of pressure shock in the piston ex¬ treme ends is reached by prepressure control. This is of signifi- cance, since in the device a relatively voluminous stream flow is utilized in relation to its size. There will be no pressure shock in the stream line, because the piston is "freely" floating.in the extreme end, i.e. it reverses along with the change of pressures active in different parts of the piston. This means that there is not an accurately determined reversal point, on reaching of which the valve would at once be mechanically closed or opened.

A further advantage of the device is its simple and solid con¬ struction and its applicability to numerous purposes. The rapid to-and-fro motion produced by the device can be utilized for pump¬ ing fluids and gases, even against great counterpressure, the de¬ vice motion can be transfered into vibration of a vibrator, stroke of a percussion machine a.s.o. On changing the ratios of piston annular sections, the piston motions can be accelerated in one di¬ rection, the motion in one direction becomes stronger as well.

In the following the invention is presented in detail with refer¬ ence to the enclosed drawing, where Fig. 1 is a section of a pump application. Fig. 2 is a section of the pump application in fig. 1 with reversing piston. Fig. 3 is a section of a valve.

Figre 1 shows an exemplary pump application of the invention. The device is a hydraulically operated pump in a pressure washer with two cylinder spaces 20. The water suction ducts are 22 and pres¬ sure channels 21. Cylinders 1 in both ends of the device. Pumping by secondary pistons 14 and 15. Secondary pistons 14 and 15 are separated from the drive fluid space 6 and 18 by packing pairs 16. Drainages 17 are between the packing pairs 16. Cylinders 1 and the body center 2 are pieces of simple cylinders. The pressure medium inlet channel is 4 and return channel 5. Inside the body center 2 there is a primary piston 3, the diameter of which actual piston part is the greatest ring shaped part. Secondary pistons 14 and 15 are fastened to primary piston 3 by thread. Figure 1 shows all pistons in motion in the arrow direction to the right. The fluid pressure is acting on the primary piston 3 ring surface A forcing the piston to the right. The pressure in chamber space 18 exits over channels 12, 10 and 7 to return pipe 5. Valve 8,9 stays on the left, while the pressure is acting on the shut- off part 9. Piston 3 travels to its extreme position on the right. The extreme position, where the piston motion reverses, is deter¬ mined by the travel of discharge channel 13 to the edge of ring chamber 19. Thereby, over discharge channel 13 full driving pres¬ sure is produced behind piston part 8 of valve 8,9 pressing the valve to the right and opening the channel closed by shut-off part 9. The gap section of piston 8 is greater than the area of gap 23 that is closed by shut-off part 9.

On rapid travel of valve 8,9 to the right, the pressure ratios on sides A and B of primary piston 3 change immediately. The shut-off part 9 opens gap 23 it has locked and piston part 8 travels to close the gap leading to the channel. Now, primary piston 3, with the pump pistons 14,15 fixed to it, reverses and starts back to the left. On sides A and B of primary piston 3 the same full pres¬ sure is active and, owing to the greater area of side B, piston 3 starts to the left by the force acting on side B. During this mo¬ tion, the fluid in chamber 6 streams out to the return line. In a combination as per figure 2, piston 3 moves to the left and fig. 2 shows a situation where the motion of pistons is just in the extreme position on the left.

Figure 2 shows valve 8,9 still in the space where pistons 3,14,15 are moving to the left. Valve part 9 is freely in the chamber. Piston 8 is pushed by full pressure to the left by a force deter¬ mined by the gap section of the shut-off gap and to the right by full pressure from the rear space of piston 8. Piston 8 keeps its position on the right till, in a situation as per figure 2, the discharge channel 13 reaches again the edge of ring chamber 6, whereat the pressure behind piston 8 sinks remarkably. Full pres¬ sure through the shut-off gap to piston 8 can now move the piston to the left shut-off position and, in its turn, the shut-off part 9 closes gap 23 and thus the situation as per figure 1 is reach¬ ed. The length of travel of the primary piston is determined by the length of shut-off part 26.

Discharge channel 13 is connected to channel 10 by a branch chan¬ nel, which has a choking section 11. With the side branch the valve function is made more reliable and thus more distinctive pressure differencies can be produced in order to move valve 8,9.

Figure 3 shows a part enlargement and section of valve 8,9 con¬ struction. The bevel surface 25 of valve 8 is tight against the corresponding seat surface of part 3. Then the pressure acting over shut-off gap 23 upon part 8 is active in piston 8 front sur¬ face only on an area as big as shut-off gap 23. Immediately, upon the slightest opening of this valve, the pressure acts rapidly al¬ so on bevel surface 25 and the force of valve 8,9 motion increases at once. The cylindrical surface of part 9 is not tight against the inner surface of opening 23 and tightening is performed with part 9 top surface 24 against part 23 front surface. With this construction reliable function of the device is achieved. Also this shut-off part acts in the same way as the valve applied to piston 8, i.e. when the shut-off part 9 closes gap 23 by means of its top surface 24 and starts to open, the pressure can act imme¬ diately by the top surface 24 on the greater ring shaped area lo¬ cated towards the centre. The force thus generated makes the mo¬ tion of part 9 to the right more effective and rapid. The above described property is most advantageously achieved in using seat valves as shown in figure 3.

The to-and-fro motion of primary piston 3 can be utilized in dif¬ ferent kinds of devices. Pistons 14,15, or only either of them, can be replaced by a moving arm coming out from the housing and the motion of it utilized. Anyway, the aim is not to restrict the device to certain applications but many modifications are possible within the inventional concept determined in the enclosed patent claims.

Claims

PATENT CLAIMS

1. A pressure medium operated device generating to-an-fro motion to one or several pistons (14,15) or a similar motion transmitting arm, comprised of a primary piston moving to-and fro in an enclos¬ ed space by means of pressure medium, and in which a control val¬ ve system (8,9) of the pressure medium that moves the primary pis¬ ton (3) is inside the said primary piston, characterized in that there are in the control valve system one or several seat valves (8), (9), the mobile part (8), (9) of which has a ring shaped tightening front surface (24), (25) on which the pressure acts immediately, when said valve opens, increasing the force that opens valve (8,9).

2. A device according to patent claim 1 characterized in that the¬ re is in the primary piston (3) a discharge channel (13), over which the increase and/or decrease of the active pressure of the medium makes valve (8,9) close or open.

3. A device according to patent claim 1 or 2 characterized in that for the channel (13), moving in primary piston (3) with respect to the body (2), a shut-off part (26) is arranged in the body to de¬ termine by its length the distance of the primary piston travel.

4. A device according to patent claim 3 characterized in that the part (26) that opens and closes channel (13) is the inner surface of the cylindrical body (2).

5. A pump working by pressure medium and consisting of a cylindri¬ cal pump body (2) , one or several to-and-fro moving pump pistons (14,15), a corresponding cylinder (1) for each piston for pumping of fluid or gas and inside the body (2) a primary piston (3) con¬ nected to the pump piston (14,15) characterized in that the prima¬ ry piston (3) has valves (8,9) for the driving pressure to trans¬ fer the pressure to both sides of the primary piston, a discharge channel (13) to control the valve (8,9) function and a part (26) to close the discharge channel (13) and to adjust the lengt of the piston stroke.

& . A pump according to patet claim 5 characterized in that there are two end to end pumping pistons (14,15), the primary piston (3) is moved by the pressure of hydraulic fluid and valves (8,9) are pressure controlled seat valves.