EP0692072B1

EP0692072B1 - Pressure medium driven device performing linear motion

Info

Publication number: EP0692072B1
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: 1999-09-15
Anticipated expiration: 2014-03-24
Also published as: DE69420713T2; WO1994021915A1; FI931324A; FI96132C; JPH08508076A; EP0692072A1; DE69420713D1; JP3538426B2; FI931324A0; FI96132B

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

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 generating the to-and-fro motion.
Previously known motion generating devices, are a.o. hydraulic cylinders working by pressure medium and different types of percussion 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, whereat the percussion machines perform, automatically, continuous to-and-fro motion. See, for example, US-A-4031812. Generally, hydraulic cylinders are controlled by means of outside valves. In percussion machines a hydraulic 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.
US-A-4031812 discloses a pressure medium operated device of the kind with which the present invention is concerned. In this prior art device a double-acting primary or working piston reciprocable in a body defining a cylinder houses a valve which controls the alternating application of the pressure medium to opposite sides of the primary piston and is itself operated by the pressure medium. The control valve comprises a valve spool which is slidable in the primary piston and on the opposite ends of which the pressure medium acts to displace the valve spool.
US-A-3788781 discloses another pressure medium operated device in which a single-acting primary or working piston houses a control valve which cooperates with the body and serves to equalize the pressures on oppositie sides of the primary piston to allow a return spring to displace the primary piston through a return stroke. US-A-4352664 discloses a similar fluid pressure operated device having a single-acting primary or working piston.
Present devices are not applicable as permanently working generators 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 improvement 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 extreme ends is reached by prepressure control. This is of significance, 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 construction and its applicability to numerous purposes. The rapid to-and-fro motion produced by the device can be utilized for pumping fluids and gases, even against great counterpressure, the device 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 direction, the motion in one direction becomes stronger as well.
In the following the invention is presented in detail with reference 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 pressure 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 determined by the travel of discharge channel 13 to the edge of ring chamber 19. Thereby, over discharge channel 13 full driving pressure 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 pressure 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 motion, 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 determined 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 pressure 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 reached. 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 channel, which has a choking section 11. With the side branch the valve function is made more reliable and thus more distinctive pressure differences can be produced in order to move valve 8,9.
Figure 3 shows a part enlargement and section of valve 8,9 construction. 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 surface only on an area as big as shut-off gap 23. Immediately, upon the slightest opening of this valve, the pressure acts rapidly also 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 immediately by the top surface 24 on the greater ring shaped area located towards the centre. The force thus generated makes the motion 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 different 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

A pressure medium operated device generating a to-and-fro movement of at least one piston (14,15) or a similar motion transmitting arm, comprising

a body (2) forming an enclosed space,

a primary piston (3) moving to-and-fro by means of a pressure medium in said enclosed space,

a control valve system (3/24, 3/25) for controlling the pressure medium to cause the to-and-fro movement of the primary piston,

characterised in that
the control valve system (3/24, 3/25) comprises two seat valves, each having a valve seat on the primary piston (3) and a movable valve member (8,9) with a pair of ring-shaped tightening front surfaces (24,25) alternately cooperating with respective associated ones of said valve seats such that when the seat valves are opened the pressure of the pressure medium acts immediately against the respective tightening surfaces to increase the force that moves the valve member.
A device according to claim 1, characterized in that there is in the primary piston (3) a discharge channel (13), over which the increase and/or decrease of the pressure of the pressure medium makes the seat valve close or open.
A device according to claim 2, characterized in that for the discharge channel (13), moving together with primary piston (3) with respect to the body (2), a shut-off part (26) is arranged in the body to determine by its length the distance of the primary piston travel.
A device according to claim 3, characterized in that the shut-off part (26) opens and closes channel (13) and is an inner surface of the cylindrical body (2).
A pump working by pressure medium and consisting of a cylindrical pump body (2), at least one to-and-fro moving pump piston (14, 15), a corresponding cylinder (20) for each pump piston for pumping of fluid or gas, and a primary piston (3) located inside the body (2) and connected to the pump piston (14, 15), characterized in that the primary piston (3) has valves (3/24, 3/25) for transferring the driving pressure of the pressure medium to both sides of the primary piston, and a discharge channel (13) to control the valve function, and in that a shut-off part (26) is provided inside the pump body (2) to close and open the discharge channel (13) to determine the length of the primary piston stroke in both directions.
A pump according to claim 5, characterized in that there are two end-to-end pump pistons (14, 15), the primary piston (3) is moved by the pressure of a hydraulic fluid and the valves (3/24, 3/25) are pressure controlled seat valves.