DE2915620A1 - Compressed air loss preventing system - increases oil volume between pneumatic and hydraulic pistons, reducing pneumatic clearance volume - Google Patents

Abstract

The process avoids the loss of compressed air, and consequently of power, corresp. to the clearance volume of a pneumatic cylinder, the latter being used to actuate a hydraulic one. The volume of oil between the hydraulic and pneumatic pistons is increased in such manner as to bring the latter piston close to the cylinder cover. Where the pneumatic cylinder slides on the piston and actuates a tappet, it is brought into a position where piston and cover touch. Pref. a third cylinder is coupled, via a stop valve, to the hydraulic cylinder chambers. The third cylinder volume can be reduced by a floating piston to zero value.

Description

Procedure for avoiding the loss of energy in the form of a

Loss of compressed air in pneumatic piston drives and devices to carry out the procedure.

When using pneumatic piston drives, especially for punching presses, is usually only part of the press stroke provided by the design during the work process used because when the stroke path is reduced, the number of strokes of the press per minute is greater will. For various reasons, the bottom dead center provided by the design is always used of the piston drive and the position of the top dead center at the distance of the reduced stroke by moving a limit switch.

This method is used in the previously known design of piston drives associated with a major disadvantage, which is that the amount of compressed air, which is located between the piston and cylinder cover at a reduced stroke height, is unused during the return stroke. This applies to both pneumatic piston drives as pressure intensifier with plunger piston and downstream hydraulic working cylinder for large press forces as well as for purely pneumatic-mechanical presses of smaller ones Power.

In both cases, this disadvantage is avoided according to the invention by that either the position of the pneumatic piston in relation to the stationary pneumatic cylinder or the position of the axially movable Pneumatikzyl inders compared to that in the upper Dead center held pneumatic piston is shifted until piston and Touch the cylinder cover, which means that the harmful space becomes zero.

The description of the device for performing the method in its application to pneumatic piston drives as pressure intensifiers with plunger pistons and the downstream hydraulic working cylinder is based on an exemplary embodiment according to Figure 1 and Figure 2, which show longitudinal sections of the device.

To achieve high mechanical forces acting over a path s, which are generated by means of a piston drive, with only a relatively low pressure of the drive medium (e.g. 6 bar compressed air) is available, is known in Way the low operating pressure by means of a pressure intensifier into a high liquid pressure transformed, which loads the piston surface of a hydraulic working cylinder.

This process is a two-fold energy conversion, which is represented mathematically as follows: p1. v1 = p2. v2 = F. s (equation 1) The following mean: p1 ..... operating pressure in bar p2 ..... liquid pressure in bar V1 ..... primary stroke volume of the pressure intensifier in cm3 v2 ...... secondary stroke volume of the pressure intensifier in cm3 F ..... mechanical force in daN s ..... ram travel in cm.

The known device with which this two-fold energy conversion is completed is shown in simplified form in Fig. 1, which is a longitudinal section shows through the intensifier and the hydraulic working cylinder.

In the pressure booster, which consists of a drive cylinder 1 and a plunger piston cylinder Inder 2 exists, the operating pressure pl of the drive piston 3 with plunger 4 pushed downwards during the work process, whereby the secondary stroke volume v2 with the liquid pressure p2 from the plunger cylinder 2, via the connecting pipe 5 is displaced into the working cylinder 6 and subsequently the working piston 7 pushes downwards with the force F.

From Fig. 1 it can be seen that the sum of the amounts of liquid, which are located in the plunger cylinder 2, in the tube 5 and in the working cylinder 6, remains constant during the work process and that it continues is a space closed to the outside for this amount of liquid. Under this condition, the amount of liquid displaced during the stroke s1 of the plunger 4 can be v2 can be equated with the following two products: V2 = A2 1 Sf = A3. s2 (equation II) This results in the relationship: A3 s (hydraulic transmission ratio) A2 s2 and s1 = s2. ü (Equation III) One could apply Equation III to others Win wise, e.g.

from the energy equation I, but the path shown here is suitable better for the following considerations. Equation 111 also applies to the total strokes h2 and h1 of the working piston 7 and the drive piston 3, h1 h2. ü from what further it can be seen that the two pistons mentioned have both the lower and the upper Always reach dead center at the same time.

The device shown in Fig. 1 is used, inter alia, as a drive set Pneumatic-hydraulic stamping presses are used, in the vast majority of cases the required mechanical working stroke s2 is smaller than the total stroke h2 of the press is. Since the time T sec for reciprocation of the working piston at a reduced Stroke s2 is smaller than the total stroke h2 of the press, increases with decreasing Stroke path the achievable number of strokes per minute and thus the number of pieces produced Stamped parts per time unit.

For this reason, the is always still permissible when installing tools The smallest stroke height s2 of the ram is set. This is done in a known manner e.g. by adjusting an electrical limit switch parallel to the ram path, by controlling the valves 9 and 10, the position of the top dead center of the piston and thus determines the stroke s2.

For punching work, but especially for the production of fine cuts, During the work process, the tool stamp 11 may only move up to the value zero Approach the upper edge of the die 12, or only a fraction of a millimeter into the die immerse. This value set when the tool is installed must be used during the working period remain. With regard to the required accuracy, this setting is used (Height of the upper edge of the die above the press table 13) always with the lower one Dead center position of the plunger 8 or the working piston 7 made because only in this Position in which the piston 7 is seated on the cylinder cover 14 which is attached to the plunger 8 Upper tool 11 has a fixed, precisely reproducible distance from the press table 13 has.

There could be other reasons why the top of the die, as a working level, must always be in the lower area of the total stroke h2.

In any case, the reduced stroke s2 is always based on the bottom dead center, by shifting the top dead center position of the working piston 7 and thus of the drive piston 3 set.

From this fact, however, results for the one shown in FIG and described device a major disadvantage that is that when Operation of the press with lifting heights s2 that are smaller than the one designed for the design Total lift height h2, considerable amounts of compressed air energy are lost because with each stroke of the cylinder chamber, which is located above the piston 3, with compressed air must be filled, which is blown out on the return stroke. If with a completely realistic one Example the total stroke h2 is 30 mm and the reduced working stroke is 5 mm and the amount of compressed air corresponding to the total stroke h1 is set at 100%, then amounts to the amount of compressed air converted into mechanical work: 5 30. 100 16.67% and the Loss amount: 100 - 16.67 - 83.33% General formula for the loss amount of compressed air in%: V - h2 s. 100 (Equation IV) h2 or V - 1 1. 100 (equation IV a) h1 the end Equation IV a shows that the loss of compressed air energy becomes zero when h1 becomes equal to s1. However, this condition is only fulfilled if at the start of the stroke the pneumatic drive piston 3 is in its structurally provided upper Dead center is (see Fig. 2) and from there covers its work path s1, which equals h1. But that means that the amount of oil remains the same and the positions of the pneumatic due to the hydraulic transmission ratio Drive piston 3 and the hydraulic working piston 7, hence the piston positions changed in the pressure intensifier compared to the positions of the piston in the working cylinder Need to become.

According to the invention, this object is achieved in that the hydraulically connected displacements of the pressure booster 2 and the work. ylinders 6 over a Shut-off element 15 is connected to at least a third cylinder displacement 14, whose Volume reduced by an adjustable floating piston 16 down to a value of zero, or up to a value that is equal to, preferably greater than, the maximum displacement of the working cylinder 6, can be enlarged, with the corresponding adjustment of the floating piston 16 by acting optionally on the one piston surface, e.g. takes place with compressed air or the other piston surface with hydraulic fluid.

The objective of this change in the piston positions according to FIG. 1 are the piston positions according to FIG. 2, in which the drive piston 3 is in its constructively intended upper ToLp.mktlage is, while the upper dead center of the working piston 7 is above the bottom dead center by the reduced stroke s2.

This change in the piston positions is brought about according to the invention in that when the shut-off device 15 is open, the manual valve 17 increases the pressure pO, which can be less than or equal to the operating pressure p1, for the floating piston releases, whereby liquid from the cylinder chamber 14 via the line 18 and the open shut-off valve 15 in the hydraulically connected displacements of the pressure intensifier and the working cylinder is pressed. When set to "Exhaust" Valves 9 and 10 is therefore the drive piston 3, as a result of pressure on the plunger 4 moved to its top dead center (touching the cylinder cover) while the working piston 7 is only up to the extent of its selected stroke s2 can approach bottom dead center, as he is at this point on a makeshift resistance which is designed e.g. as a simple plate with the thickness s2, which is between Die 12 and upper tool 11 come to rest.

With the same objective, the change in the piston positions could by means of the same device can also be done in a different way, e.g. the extreme position of the pistons 3 and 7, in which the drive piston 3 is in its top dead center position and the working piston 7 is in its bottom dead center position occupies. Via the valve 10, which is otherwise used to return the working piston 7 and the drive piston 3 is open, pressure medium is also in this case in initiated the cylinder space below the working piston 7. As the drive piston 3 is located with plunger 4 in top dead center and therefore the fluid pressure cannot give way is activated by the working piston during the adjustment process 7 as long as liquid from the hydraulically connected displacements of the pressure booster and the working cylinder via the open shut-off element 15 and through the pipeline 18 is displaced into the third cylinder displacement 14 until the reduced lift height s2 is reached is. The manual valve 17 is set to "exhaust". If the intended lifting height S2 reached and so that the adjustment work is finished, the shut-off device 15 is closed.

The swept volume of the third swept volume 14 is advantageously larger selected as the maximum stroke volume of the hydraulic working cylinder 6. The excess Liquid is used to compensate for any leakage losses. This compensation is at made the extreme position of the piston described above.

The device according to the invention is characterized by its simple design Structure and easy handling. When changing the piston positions only one measurement is required, namely that of the reduced working distance s2. The corresponding positions of the drive piston 3 and the working piston 7 at which no compressed air loss occurs are reached automatically.

The device according to the invention is from the control of the press independent. It can therefore be used as an additional device without difficulty and effort connected to any existing press that works according to the principle described will.

In addition to the considerable savings in compressed air energy, the inventive Device the possibility of an automatic leak oil compensation.

The description of the device for performing the method in its application to pneumatic-mechanical piston drives with working rams on the basis of an exemplary embodiment according to FIGS. 3 and 4, the partial longitudinal sections show through a punch press.

The pneumatic-mechanical piston drive shown in FIGS. 3 and 4 consists, for example, of two pistons whose mechanical forces add up. In the case of small forces, a piston could also be sufficient, or it would also be more than two pistons required. The number of pistons is for the process according to the invention and its device is irrelevant.

The cylinder cover 20, the intermediate floor 21 and the cylinder floor 22 are joined together with lag screws, not shown. The cylinder bottom 22 is started with a sleeve-shaped extension 23, which on the one hand to Fühning of the press ram 24 is used and on the other hand in a cylindrical recess 25 of the press yoke 26 is slidably mounted. For fixing any set distance of the cylinder base and thus of the whole Cylinder system for the yoke plate 26 and for power transmission, serve at least two, preferably more than two threaded spindles 27 which are fastened in the press yoke 26, through holes in the cylinder base and each with a nut 28 and a lock nut 29 are equipped, which, as FIG. 4 shows, at any point on the threaded spindle can be tightened.

The movable press ram 24 with piston, for example with a Bärplatte 30 is firmly connected, which is guided by the tie rods 31 of the press and the upper tool 32 carries, is for the purpose of performing the later described Adjustment work on the one hand, for example through a makeshift intermediate layer 33 in the form of a plate, the thickness of which corresponds to the desired stroke s and on the other hand by adjusting rings 34, which hold down the bear plate together with the plunger and piston, in locked in its position. The procedural shift of the pneumatic cylinder inders compared to the stationary piston until it is shown in FIG. 4 to a contact between The cylinder cover and piston are delivered pneumatically by means of pressure being fed into the Cylinder space 35, below the piston. The opposite cylinder movement can optionally by supplying pressure into the cylinder space 36 above the piston be evoked.

Claims (5)

PATENT CLAIMS 4). Procedure to avoid the loss of energy in the form of a lost amount of compressed air that corresponds to the displacement part not used by the piston of a pneumatic cylinder, this harmful space between the cylinder cover, as a mechanical stroke limiter and the piston is located when it is in a dead center position is located3 which corresponds to a stroke that is smaller than that intended by the design Overall nub is characterized in that pneumatic piston drives are used as Pressure intensifier with plunger piston and downstream hydraulic working cylinder, by the position of the hydraulic working piston and by the hydraulic one Position of the pneumatic piston due to the transmission ratio by enlarging it the amount of oil between the plunger and the hydraulic working piston the pneumatic cylinder fastened in the frame is as close as possible to the cylinder cover and that in the case of pneumatic piston drives with working ram3 the one in the frame Pneumatic cylinder displaceable coaxially to the piston at any point its stroke is moved so far that the piston is held and cylinder cover touch. 2 device for performing the method according to claim 1 for Change in the piston position of a pressure intensifier compared to the piston position a working cylinder hydraulically connected to it, characterized in that to the hydraulically connected cubic capacity of the pressure booster and the working cylinder At least a third cylinder displacement is connected via a shut-off device, its volume by an adjustable floating piston up to that The value is reduced to zero, or to a value that is the same, preferably greater than the maximum displacement of the working cylinder can be increased, wherein the corresponding adjustment of the floating piston by acting optionally one piston surface with compressed air or the other piston surface with hydraulic fluid he follows. 3. Apparatus for performing the method according to claim 1 for Displacement of a pneumatic cylinder displaceable coaxially to the piston opposite dem3 piston held at any point of its stroke characterized by: that the bottom of the pneumatic cylinder 22 is in the press yoke 26 by means of a sleeve 23 is slidably mounted and the cylinder at any distance from the press yoke for example by at least two threaded spindles fastened in the press yoke 27, with nut 28 and lock nut 29, between which the flange of the cylinder base is clamped, is held in a force-transmitting manner. 4. Apparatus according to claim 1 and 3, characterized in that the movable ram 24 during the displacement of the pneumatic cylinder in its 3 the working path s corresponding dead center position in the press frame, for example an intermediate layer 33 in the tool and held by adjusting rings 34 on the tie rods 31 will. 5. Apparatus according to claim 1, 3 and 4 characterized gekennzeichnec that the pneumatic cylinder is moved pneumatically in both directions, inclsm either the lower piston surface 35 or the upper piston surface 36 with compressed air is applied.