Method for Controlling Delivery Quantity, and Reciprocating Compressor Having Delivery Quantity Control

Abstract

The invention relates to a method for delivery quantity control of a reciprocating compressor, wherein the motion of a closing organ (5b) of an automatic suction valve (5) is influenced during at least one part of a cycle of the crankshaft by means of a refraction gripper (6), wherein the method comprises a continuously variable return flow control, wherein the retraction gripper (6) contacts the closing organ (5b) and prevents the same from closing during a first partial segment (K1) of the cycle of the crankshaft, and wherein the retraction gripper (6) is retracted during a second partial segment (K2) of the cycle of the crankshaft and the closing organ (5b) is closed, wherein the retraction gripper (6) is retracted such that the speed of the moving closing organ (5b) is reduced prior to contacting the suction valve (5).

Description

The invention concerns a method for controlling delivery quantity of a reciprocating compressor according to the preamble of claim 1. The invention further concerns a reciprocating compressor with delivery quantity control according to the preamble of claim 12.

BACKGROUND ART

Documents EP 0 801 227 A2 and EP 1 400 692 disclose a method for influencing the pressure-dependent, self-acting, periodic opening movement of a closing body of an intake valve of a reciprocating compressor by means of a control device which influences the closing body, as necessary, over at least a part of the crank rotation. Since the service life of self-acting compressor valves, as mostly used on the intake and the pressure side, is primarily influenced by the impact-stress-requirement of the alternating impingement of the actual closing body on, respectively, the seat or backstop, the above-mentioned documents disclose a method in which the intake valve is forcefully opened before reaching pressure equilibrium by using a so-called unloader (or ‘lift off gripper’), in order to avoid a sharp, instantaneous acceleration of the closing body towards the backstop, which would occur upon automatic opening. This enables reduction of the impact-stress-requirement of the compressor valve.

This method has the disadvantage that the compressor valves, as used on the intake side and, in particular, those used on the pressure side, still have a high stress-requirement, particularly when the compressor system is run using continuously variable backflow regulation methods. With continuously variable backflow regulation, the intake valve is held open with the help of the unloader during a partial angular range of the compression cycle and is thereafter shut, in order to thereby influence the delivery quantity.

A disadvantage of this known method is the fact that the closing body of the intake valve and of the pressure valve is subject to relatively high wear, which requires a correspondingly high maintenance effort.

PRESENTATION OF THE INVENTION

The problem to be solved by the invention is to provide a more advantageous method for controlling delivery quantity of a reciprocating compressor. This problem is solved by a method having the features of claim 1. Dependent claims 2 to 11 concern further advantageous method steps. The problem is further solved by a reciprocating compressor having the features of claim 12. Dependent claims 13 to 17 concern further, advantageous embodiments.

In particular, the problem is solved by a method for delivery quantity control of a reciprocating compressor, in which the movement of a closing body of a self-acting intake valve is influenced during at least part of a cycle of crank rotation by an unloader driven by a control device, wherein the method comprises a continuously variable backflow regulation, in which the unloader lies against the closing body during a first section of the cycle of crank rotation and prevents its closure, and in which the unloader is driven back during a second section of the cycle of crank rotation and the closing body is closed, wherein the unloader is driven back in such a way that the speed of the moving closing body is reduced prior to its seating on the intake valve.

In a further advantageous method, this comprises a skip regulation, in which the unloader prevents closure of the closing body during a whole cycle of crank rotation, wherein the delivery quantity is regulated by at least a combination of continuously variable backflow regulation and skip regulation.

In the method according to the invention, the delivery quantity is regulated by the forced holding open of the intake valve. In the course of doing this, preferably two different regulation methods are used, namely a skip regulation and the continuously variable backflow regulation. Both methods employ a so-called unloader, which presses the closing body of the valve, for example a plate valve, ring valve or poppet valve, into an open position and preferably, onto the valve seat.

The reciprocating compressor has a compression space, to which gas is introduced via an intake valve and from which compressed gas is led away via an outlet valve, also called pressure valve. In the skip regulation method, the closing body of the intake valve is held open during a whole working stroke or a complete work cycle. This causes the pressure in the compression space to not rise above the pressure required to open the pressure valve during the compression phase, such that the aspirated gas is pressed back into the intake conduit during the compression phase and thus compression and further transport into the pressure conduit are not available. The pressure valve thus remains shut and thus this compression space does not convey any gas via the pressure valve into the pressure conduit. If skip regulation is deactivated, i.e. normal operation executed, then the compression space again conveys the whole gas stream via the pressure valve into the pressure conduit. If the reciprocating compressor has, for example, only one compression space, then skip regulation may be run such that certain working cycles are executed normally and skip regulation is activated during certain working cycles. In this way, a disadvantage of skip regulation is that the amount of gas conveyed from the reciprocating compressor can only be regulated in a stepwise manner. A further disadvantage of skip regulation is that there is no flow through the unloaded compression space, i.e. with non-opening pressure valve, and thus dirt can collect in the compression space, which raises valve wear or respectively wear of the packing rings and piston rings.

In the backflow regulation method, the intake valve is held open with the help of the unloader during a partial angular range of a complete compression stroke or respectively of a complete crank rotation and thereafter is shut, in order to thereby influence the delivery quantity. In doing this, the intake valve is only pressed open by the unloader at the beginning of the compression phase. In this way, a part of the gas in the compression space is pressed back into the intake conduit. As soon as the closing body of the intake valve completely closes, the gas remaining in the compression space is compressed and pressed into the pressure conduit via the pressure valve. In this way, during backflow regulation, only a part of the maximum-possible gas stream is conveyed from the compression space into the pressure conduit via the pressure valve.

With the backflow regulation method, the fact that the opening time of the self-acting pressure valve is reduced proportionately for smaller delivery quantities is disadvantageous, as is the fact that for delivery quantities of less than 40% of the rated delivery quantity the opening time of the pressure valve is reduced to such an extent that the opening and shutting speeds of the pressure valve can increase by multiples. On the one hand, this leads to increased wear of the self-acting pressure valve and, on the other hand, this reduces the range within which partial delivery quantities may be reliably conveyed. A further disadvantage of backflow regulation is that the gas is more strongly heated prior to compression due to the longer dwell time in the compression space and due to heat transfer via the cylinder wall and due to a leak stream via the piston. This results in the gas on the pressure side having a raised temperature.

In an advantageous embodiment, the method according to the invention has the advantage that, through combined use of back flow regulation and skip regulation, the quantity delivered by the reciprocating compressor can be varied across a wide range, in particular with no additional wear of the closing body of the intake valve and/or pressure valve. For regulation of the delivery quantity, there are essentially preferably three different methods available which may be used. Alongside a method with maximal delivery quantity, in which the intake valve shuts automatically, also the backflow regulation method as already described and the skip regulation method as already described. For example, regulation dependent on the quantity of fluid to be delivered at any particular time may be brought about as follows:

• • For delivery of the maximal delivery quantity, no influence is exerted on the intake valve, which thus opens and closes in a self-acting manner.
  • For large delivery streams, i.e. delivery quantities in the range of between about 100% and 80% of the maximal delivery quantity, continuously variable backflow regulation is deployed. Although it is also possible that not every cycle of crank rotation is regulated with backflow regulation, but rather that the intake valve is operated automatically (i.e. without exerting influence), for example , for one or two cycles. This method has the advantage that the unloader is called for less such that longer service life results and that quantity regulation itself uses up less energy.
  • For medium-sized delivery streams, i.e. with delivery quantities in the range of between about 80% and 50% of the maximal delivery quantity, continuously variable backflow regulation is used for each cycle.
  • For small delivery streams, i.e. with delivery quantities in the range of between about 50% and 0% of the maximal delivery quantity, the closing body of the intake valve is held open during, for example, one or two cycles, by means of skip regulation. For the other cycles, the intake valve can either be operated in a self-acting way or, additionally, if required, backflow regulation may be deployed.

It is particularly advantageous for the intake valve to be influenced by the control device and the unloader such that the closing body of the pressure valve of the reciprocating compressor is opened during at least a predetermined range of opening angle of crank rotation. The range of opening angle is at least 10° and preferably at least 20° to 30°.

Both of the method according to the invention and the reciprocating compressor according to the invention have the advantage that the stroke movement and/or the speed of the unloader is very precisely controllable with the help of a drive mechanism, preferably an electromagnet, in such a way that the closure speed of the closing body can be reduced prior to its seating on the intake valve, such that the closing body impinges on the intake valve at limited speed and comes to rest there such that the closing body thus seats ‘gently’ on the intake valve, which can be referred to in English as a ‘soft landing’. In a particularly preferred method, the speed of the closing body during seating on the intake valve is less than 0.1 m/s, such that the closing body 5b has a permitted impingement speed of less that 0.1 m/s during impingement on the valve seat 5a of the intake valve 5. This advantageous method reduces wear of the closing body considerably and, more advantageously, additionally results in operation of the valve having a low noise level.

In a further advantageous embodiment, the drive mechanism comprises a controllable damping mechanism, in order to influence the speed of the unloader and, in particular, the location of reduced speed, such that the closing body impinges on the intake valve with limited speed when closing, such that the closing body thus seats ‘gently’ on the intake valve and shuts it. It is particularly advantageous both that the damping mechanism be electrically controllable and that it comprises an electrorheological or magnetorheological fluid, whose viscosity is electrostatically or electromagnetically variable, such that damping is very quickly variable via electrical signals. The damping mechanism can however also be based on another principal and for example may take the form of an electromagnet.

The invention is described in detail in the following with the help of embodiment examples.

SHORT DESCRIPTION OF THE DRAWINGS

The drawings used for explanation of the embodiment examples show:

FIG. 1 a longitudinal cross-section through a controllable valve;

FIG. 2 an example of the movement of the unloader, of the closing body of the intake valve as well as the speed of the unloader as a function of crank angle;

FIG. 3 the progression of pressure in the compression space of the reciprocating compressor for differing operating methods;

FIG. 4 the progression of valve travel of the intake valve and of the pressure valve for the operating methods shown in FIG. 3;

FIG. 5 a load progression in a PV-diagram for differing operating methods;

FIG. 6 characteristic variables of the valve as a function of crank angle;

FIG. 7 schematically a reciprocating compressor;

FIG. 8 schematically a control device for operation of the gripper acting on the intake valve;

FIG. 9 schematically a further control device for operation of the gripper acting on the intake valve.

In principle, the identical parts are provided with the same reference signs in the drawings.

WAYS OF CARRYING OUT THE INVENTION

FIG. 1 shows a longitudinal cross-section through a controllable valve 1 comprising a compressor housing 4 with an intake valve 5 arranged therein, whose position is influenced by an unloader 6, wherein the unloader 6 is actuated by a control device 2, arranged outside of the compressor housing 4, via a connection means 7, in the form of a connection rod.

The compressor housing 4 comprises a lamp 4a, a gas space 4b, a compression space 4c and a cover 4d, wherein the compressor housing 4 also comprises a non-depicted or, as the case may be, an unseen pressure valve 8, via which the compressed fluid may escape from the compression space 4c. The self-acting intake valve 5 comprises a valve seat 5a, a closing body 5b, which is mounted so as to be movable in a stroke direction B and is referred to in the following as valve plate 5b, a valve backstop 5c, as well as a return spring 5d. The unloader 6 comprises a plurality of gripper extensions 6a or fingers 6a, a guide 6b as wells as a pressure spring 6c. The unloader 6 is slidably mounted in stroke direction B, driven by the electromagnet 2a, wherein the tip of the gripper extensions 6a can lie against the valve plate 5b, depending on the stroke in direction B, and in particular, can push the valve plate 5b against the valve backstop 5c, such that the valve plate 5b is no longer movable, and the valve 5 thereby stays open by force. The control device 2 comprises an electromagnet 2a, as a driving mechanism, with a magnet anchor 2b, a magnet core 2c as well as a magnet coil 2d. The control device 2 further comprises a housing 2m, which is connected with the compressor housing 4 via a connection part 2e. The control device also comprises a steering mechanism 2i or a regulating mechanism 2i, electrical conductors 2k, 2l, wherein the electrical conductor 2l connects the steering mechanism 2i with the electromagnet 2a. The control device 2 comprises two guides 2f, 2g to mount the electromagnet 2a and the connection rod 7 slidably in stroke direction B. A filter 3 can also be provided. In an advantageous embodiment, the control device 2 also comprises a displacement sensor 2h, which captures the stroke or, respectively, the position of the electromagnet 2a or, respectively, the position of the unloader 6 in stroke direction B.

The controllable valve 1 shown in FIG. 1 can now be steered via the cycles of crank rotation in different ways. A cycle is to be understood as a 360° rotation of the reciprocating compressor crankshaft.

FIG. 2 shows the operation of a continuously variable backflow regulation, wherein what is shown in FIG. 2 are the stroke movement A of the unloader 6, the stroke movement B of the valve plate 5b and the speed C of the unloader 6 as functions of the crank angle, wherein a single rotation of the crankshaft is depicted, i.e. FIG. 2 shows angular progression from 0° to 360°. It can be seen from the valve plate's 5b stroke movement B, that the valve plate 5b automatically opens during the intake, in the angular range of about 90° to 110° in the embodiment example shown, such that the valve plate 5b lies against the valve backstop 5c. In the operation of the continuously variable backflow regulation, after opening of the valve plate 5b, the unloader 6 is moved or, respectively, made to travel, as depicted by way of example by curve A, until it lies against the valve plate 5b. The speed of the unloader 6 is also shown in FIG. 2 by curve C. When operating in self-acting mode, the intake valve 5 would automatically shut when the piston changes direction—at 225° in the example shown. Thus, the operation of a continuously variable backflow regulation has the effect, that the unloader 6 lies against the closing body 5b, during a first section K1 of the cycle of crank rotation, and prevents its shutting, and that the unloader 6 is driven back according to the progression of curve A2, during a second section K2 of the cycle of crank rotation, wherein, due to the prevailing pressure conditions, the closing body 5b, namely the valve plate 5b, follows the movement of the unloader 6 or, respectively, lies against the unloader 6, such that the valve plate 5b lies on the valve seat 5a at some point in time—at about 290° in the example shown—and shuts the valve 5. In the further section K3, the unloader 6 is made to travel still further, so that it, for example, is distanced from the valve plate 5b.

The movement of the closing body 5b is influenced in section K2 by the drive mechanism, in the embodiment example shown by the electromagnet 2a and the connection rod 7, in such a way that the unloader 6 has, as a function of crank rotation, the progression of travel A shown in FIG. 2 or, respectively, the progression of speed C shown in FIG. 2, wherein the electromagnet 2a is steered in such a way that the speed of the moving closing body 5a is reduced prior to seating on the intake valve 5, as is shown in FIG. 2. In a particularly advantageous embodiment, the unloader 6 is even thereafter made to travel into an end position in a further section K3, advantageously as shown in curve C by the “second hump”, in which another acceleration followed by another braking occurs, such that the unloader 6 comes to rest, as shown by progression of travel A at section K3, at a distance from, i.e. without direct contact with, the closing body 5a. In an advantageous method step, the electromagnet 2a is steered such that the closing body 5b has a speed of less than 0.1 m/s while seating on the intake valve.

The valve 1 can also be operated by skip regulation methods. With skip regulation, the unloader 6 is made to travel in such a way that it prevents shutting of the closing body 5b for the duration of a whole cycle of crank rotation, advantageously in such a way that the unloader 6 lies against the closing body 5b during the whole cycle, such that the latter remains opened over the whole cycle.

FIG. 7 shows schematically a reciprocating compressor comprising a compressor housing 4 with a movably mounted piston 4e, which, in part, delimits a compression space 4c, and which is driven by a piston rod 4f. On the compressor housing 4, there is also an intake valve 5, via which the fluid or gas, which is to be conveyed, is aspirated. The reciprocating compressor also comprises a gripper 6, which is driven by a control device 2 comprising a drive mechanism. The control device 2, the intake valve 5 and the gripper 6 form a controllable valve 1. On the compressor housing 4, there is also a pressure valve 8, via which the compressed gas leaves the compression space 4c. The reciprocating compressor can, of course, also comprise a plurality of compression spaces 4c, wherein each compression space 4c comprises a separate piston 4e with piston rod 4f, and wherein each compression space 4c comprises a separate, controllable valve 1.

FIG. 3 shows now the progression of pressure in a compression space 4c of a reciprocating compressor as a function of crank angle for differing operating methods. In the embodiment example shown, bottom dead centre, U_TP, lies at 90°, i.e. at this position the compression space 4c reaches maximum volume. Top dead centre, O_TP, lies, in this example, at 270°, i.e. at this position the compression space 4c reaches minimum volume. In the first section D, the movement of the closing body 5b of the intake valve 5 occurs automatically, resulting in the shown progression of pressure over a 360° crank angle. Movement of the closing body of the pressure valve 8 always occurs automatically in FIG. 3. In the embodiment example shown, the pressure on the pressure side is, for example, about 3.1 bar, wherein the pressure valve 8, in the embodiment example shown including valve spring biasing, opens itself at a pressure of about 3.2 bar. The pressure valve 8 opens at, say, a crank angle of 190°. The self-acting pressure valve 8 is completely opened, in the depicted embodiment example, during an angular range K_w of about 50° because the pressure valve 8 has maximal valve travel in this maximally-open-angular-range K_w, before the pressure valve 8 closes again. The total opening angle K_v, during which the valve is open, i.e. the closing body is lifted from the valve seat, or, respectively, the total opening time of the pressure valve 8 is appx. 80°. In the second section E, a skip regulation is depicted, during which, as previously described, the closing body 5b is held open over the whole crank angle of 360°, resulting in the shown progression of pressure in the compression space 4c. The pressure in the compression space 4c remains at all times below 3.2 bar, such that the pressure valve 8 does not automatically open. In the third section F, a continuously variable backflow regulation is depicted, during which, as described in FIG. 2, the closing body 5b is held open by the unloader during a part of the crank angle of 360°, such that the accumulation of pressure in the compression space 4c occurs later in relation to crank angle, resulting in the shown progression of pressure. The pressure valve opens at, say, a crank angle of 210°. The self-acting pressure valve 8 remains completely opened in the depicted embodiment example during a maximally-open-angular-range K_w of about 30° before the valve travel reduces, as shown in FIG. 4, and the valve 8 completely closes again after the total opening angle K_v. The total opening angle K_v, during which the valve is opened, or, respectively, the total opening time of the valve is appx. 60°.

With skip regulation, the intake valve 5 is thus held open during a complete working stroke. In this way, the aspirated gas is pressed back into the intake conduit during the compression phase and thus is not available for compression and further transport in the pressure conduit. The compression space does not convey any gas. If skip regulation is deactivated, the compression space once again conveys the full fluid stream.

By contrast, with constantly variable backflow regulation, the closing body 5b of the intake valve 5 is only pressed open for the beginning of the compression phase. In this way, a part of the gas is pressed back into the intake conduit. If the intake valve 5 shuts, then the gas remaining in the compression space can be compressed and pressed through the pressure valve into the pressure conduit. The compression space only conveys a part of the maximum-possible gas stream.

Both methods use the unloader 6 to press the sealing element 5b of the valve 5, for example a plate, ring or poppet valve, against the valve backstop 5c and thus into the open position. Since for constantly variable backflow regulation, in one working cycle, the unloader 6 has to be moved from the closed to the open position and back again, and since for skip regulation a longer time is available for the same sequence of movements, the power uptake, the required forces, the travelling speeds and the stress-requirements of the parts used are higher for constantly variable backflow regulation.

As indicated in FIG. 3, the delivery quantity of a reciprocating compressor can now be regulated over a wide range by a combination of constantly variable backflow regulation F and skip regulation E, wherein, beyond this, section D can also be used for delivery quantity regulation, during which the closing body moves automatically. These three types of actuation D, E, F of the operation of valve 5 can now be combined together in any desired manner, such that, for example, initially during successive cycles only actuation type D, E or F occurs and later on, for example, a combination of at least two of the three actuation types D, E and F.

For example, the valve could be steered in such a way that various delivery quantities are regulated in such a way, that, for large delivery streams, the intake valve 5 is automatically driven during certain cycles and is driven with constantly variable backflow regulation during certain cycles; that, for middle-sized delivery quantities, the intake valve 5 is driven during every cycle with constantly variable backflow regulation; and that, for small delivery quantities, the intake valve 5 is constantly held open during certain cycles, and driven with constantly variable backflow regulation during certain cycles.

FIG. 4 shows the stroke movement 8c of the pressure valve 8 as a function of crankshaft angle. The stroke movement 5e of the closing body 5b of the intake valve 5 is also shown as a function of crankshaft angle. Movement of the pressure valve 8 occurs automatically, whereas, as previously described, movement of the closing body 5b of the intake valve 5 is determined by the gripper 6 with skip regulation E and backflow regulation F. In FIG. 4, the maximally-open-angular-range K_w is well-recognisable, within which the valve 8 has a maximal valve stroke, i.e. is maximally opened. Also visible is the total opening angle K_v, during which the valve 8 is opened.

The duration of opening of the self-acting pressure valve 8 is determined by the angular range, during which the pressure in the compression space 4c lies above the opening pressure of the pressure valve 8; in the embodiment example of FIG. 3 above a pressure of 3.2 bar. From the constantly variable backflow regulation shown by F in FIGS. 3 and 4 it may be seen that the later the closing body 5b is shut, the more the angular range of opened pressure valve 8 reduces itself. Especially with small delivery quantities, this has the result that, if backflow regulation were constantly used then the pressure valve 8 would only be opened during a very short total opening angle K_v. In order to raise the total opening angle K_v of the pressure valve 8 with small delivery quantities, the reciprocating compressor is run in such a way that skip regulation E is used during one or several crank cycles, in order to convey a sufficiently large quantity of gas in the succeeding backflow regulation F, such that the pressure valve 8 remains opened over a total opening angle K_v of at least 10° and preferably over a total opening angle K_v of at least between 20° and 30°. This results in the pressure valve 8 being opened long enough to avoid excessive strikes or excessive opening and shutting speeds. This extends the operating life of the pressure valve considerably. FIG. 5 shows a load progression in a PV-diagram under different operating methods, namely as already shown in FIG. 3, at full load D with self-acting intake valve 5, with skip regulation E and with constantly variable backflow regulation F.

A compressor can be arranged such that, as shown in FIG. 7, it has only one compression space 4c per cylinder, wherein, in the following, such a compression space is also referred to as upper compression space. A compressor can also be arranged such that it has a second compression space in the same cylinder, which is separated from the first compression space by the piston 4e, such that during movement of the piston 4e, the fluid in one compression space is compressed and in the other compression space is aspirated. In the following, the second compression space is also referred to as lower compression space. In a particularly advantageous method, delivery quantity regulation occurs as indicated in FIG. 3 such that the pressure valve 8 of the reciprocating compressor opens at least during a predetermined angular range Δ of 20° to 30° before reaching top dead centre O_TP (for the upper compression space) respectively bottom dead centre U_TP (for the lower compression space, in the case of the cylinder comprising two compression spaces) of the crank rotation. The advantage of this method is that only the timing of opening needs to be determined, since the timing of shutting is known to some degree and for an idealised valve, lies at dead centre of the upper or, respectively, if present, lower compression space.

The opening time of the pressure valve 8 can, for example, be determined by measuring the pressure in the compression space and comparing this with the final pressure, or given knowledge of the operational conditions of the compressor, by a previous, respectively simultaneous calculation of the maximal opening time of the intake valve around the reversal point of piston movement, so that the pressure valve's minimal opening time is not fallen below.

FIG. 6 show characteristic variables of the controllable valve 1 as a function of crank angle, respectively, angle of rotation, for obtaining the progression of movement B of the valve plate 5b and the progression of movement A of the unloader 6 as shown in the path diagram in FIG. 6. The progression of the speed of the unloader 6 is also shown in curve C. Also, the force G applied by the electromagnet 2a is shown in curve G and the required current H for steering of the electromagnet 2a is shown. The progressions shown in FIG. 6 are, in particular, important in bringing about the ‘gentle landing’ of the valve plate 5b on the valve backstop 5c set out in FIG. 2.

FIG. 8 shows schematically a further embodiment example of a control device 2 for actuating and driving the gripper 6 acting on the intake valve 5. The control device 2 comprises a drive mechanism 2n, which is connected with the gripper shown schematically in FIG. 7 via the connection rod 7, which is mounted so as to be linearly movable. The drive mechanism 2n shown in this embodiment example comprises a linear drive 2w as well as a steerable damping mechanism 2o, wherein the damping mechanism 2o has the task of damping motion produced by the linear drive 2w in an electrically steerable way such that the gripper 6 respectively the valve plate 5b of the intake valve 5 moves as, for example, shown in FIG. 2. The linear drive 2w has a linearly movable connection rod 2t, which is functionally connected with the connection rod 7. In the embodiment example shown, the damping mechanism 2o is arranged between the linear drive 2w and the gripper 6. The damping mechanism 2o could however also be arranged at another position, for example, in the depicted view of the control device 2, also above the linear drive 2w. The damping mechanism 2o can take many different possible forms to be able to effect a damping of the motion of the linear drive 2w. The damping mechanism 2o shown schematically in FIG. 8 is particularly advantageous for bringing about the ‘gentle landing’ of the valve plate 5b on the valve backstop 5c as per the invention. The damping mechanism 2o comprises a cylinder 2p and internal to this a linearly slidable piston 2r, which divides the internal space of the cylinder 2p into a first internal space 2q and a second internal space 2s. The two internal spaces 2q, 2s are connected to each other via a fluid-conducting connection 2u, such that a fluid is exchangeable between the two internal spaces 2q, 2s. In an advantageous embodiment, the two internal spaces 2q, 2s are fluid-conductively connected with each other via an electrically steerable damping or choke 2v. A steering and regulating device 2i is signal-conductively connected with both the linear drive 2w and the steerable damping 2v via electrical conductors 2k, 2l, such that both the linear drive 2w and the damping properties of the damping mechanism 2o are steerable, in order to steer the position or, respectively, the speed of the valve plate 5b in such a way that a ‘gentle landing’ of the valve plate 5b is achieved, as shown by way of example in FIG. 2.

The fluid conductive connection 2u as well as the electrically steerable damping 2v could also be arranged on the damping mechanism 2o of inside the damping mechanism 2o, in particular, also at the piston 2r, by providing the piston 2r, for example, with a fluid-conductive connection between the first and second internal space 2q, 2s.

In a particularly advantageous embodiment, the fluid of the damping mechanism 2o consists at least partially of an electrorheological or magnetorheological liquid. Such liquids have the property that their viscosity is electrically steerable, such that with such liquids, an electrically-controllable choking section can be brought about. Such a choking section has the advantage that the viscosity can be varied over a wide range and that the viscosity can be varied very quickly with the help of an electrical signal. The damping properties of such a damping mechanism 2o are thereby very rapidly variable, such that the movement of the piston 2r and therewith the movement of the connection rod 7, of the gripper 6 and ultimately of the valve plate 5b can be damped or, rather, can be steerable and regulatable, in such a way that the valve plate 5b carries out a ‘gentle landing’ with respect to distance travelled and speed.

Damping mechanisms comprising an electrorheological or magnetorheological liquid are, for example know from the document WO 2008/141787A1 or from the document EP 1 034 383 B1.

The linear drive 2w can take the form of, for example, an hydraulic or pneumatic drive, an electromagnetic drive, a linear motor or an electrical motor with a transmission.

FIG. 9 shows a further embodiment example of a control device 2. In contrast with the embodiment shown in FIG. 8, the damping mechanism 2o in FIG. 9 comprises an electrically controllable three-way valve 2y, a non-variable choke 2x as well as fluid conduits 2u₁ and 2u₂. The damping properties of the damping mechanism 2o are controllable via the electric three-way valve 2y, through the latter allowing the fluid which is exchanged between the first and second internal space 2q, 2s flow either via fluid conduit 2u₁ or fluid conduit 2u₂ and the choke 2x. The damping mechanism 2o could also comprise a plurality of chokes 2x with various choking effects, as well as a multi-port valve, which can controllably and selectively guide the fluid to each of these chokes, such that the damping mechanism 2o has a plurality of different dampings.

In a further advantageous embodiment, the damping mechanism 2o could be arranged such that the braking energy that is given up by the damping mechanism 2o to the closing body 5b can be recovered. For example, the damping mechanism 2o could be an eddy current brake. The damping properties of such an eddy current brake could also be electrically controllable. In a particularly advantageous embodiment, the damping mechanism 20 thus takes the form of a controllable eddy current brake, which, on the one hand, allows a steering of the damping properties and which, on the other hand, allows energy recovery, wherein for energy recovery, electrical energy is produced by preference. Since the unloader 6 is operated very quickly and very often during backflow regulation, a damping mechanism 2o with energy recovery is particularly advantageous for reducing the overall energy demand for intake valve 5 operation or, respectively, for operation of the unloader 6. Also warming, which occurs during operation, is advantageously reduced.

Claims

1. Method for delivery quantity control of a reciprocating compressor, in which the movement of a closing body (5b) of a self-acting intake valve (5) is influenced during at least part of a cycle of crank rotation by an unloader (6) driven by a control device (2), wherein the method comprises a continuously variable backflow regulation, in which the unloader (6) lies against the closing body (5b) during a first section (K1) of the cycle of crank rotation and prevents its closure, and in which the unloader (6) is driven back during a second section (K2) of the cycle of crank rotation and the closing body (5b) is closed, wherein the unloader (6) is driven back in such a way that the speed of the moving closing body (5b) is reduced prior to its seating on the intake valve (5).

2. Method for delivery quantity regulation according to claim 1, characterised in that the method comprises a skip regulation, in which the unloader (6) prevents closure of the closing body (5b) during a whole cycle of crank rotation, wherein the delivery quantity is regulated by at least a combination of continuously variable backflow regulation and skip regulation.

3. Method according to claim 1, characterised in that, during seating on the intake valve (5), the speed of the closing body (5b) falls below a permitted impingement speed, and that this is less than 0.1 m/s.

4. Method according to claim 1, characterised in that, after the seating of the closing body (5b), the control device (2) moves the unloader (6) still further and then brings it to rest, in order to distance the unloader (6) from the closing body (5b) and to bring the unloader (6) to an end position.

5. Method according to claim 1, characterised in that, after the seating of the closing body (5b), during a third section (k3) of the crank rotation, the control device (2) once again accelerates the unloader (6) and then brings it to rest, in order to distance the unloader (6) from the closing body (5b) and to bring the unloader (6) to an end position.

6. Method according to claim 1, characterised in that, the control device (2) comprises an adaptive pre-control with which the stroke (A) and the speed (C) of the unloader (6) are regulated.

7. Method according to claim 1, characterised in that, the intake valve (5) is influenced by the control device (2) and the unloader (6) in such a way that a closing body (8b) of a pressure valve (8) of the reciprocating compressor is opened during at least a predetermined total opening angle (Kv) of a crank rotation.

8. Method according to claim 7, characterised in that, the predetermined total opening angle (Kv) is at least 10°, and preferably lies at least in the range between 20° and 30°.

9. Method according to claim 1, characterised in that, the intake valve (5) is influenced by the control device (2) and the unloader (6) in such a way that a closing body (8b) of a pressure valve (8) of the reciprocating compressor is opened at least during a predetermined angular range (Δ) of a crank rotation before the upper, respectively lower dead centre (OTP, UTP).

10. Method according to claim 9, characterised in that, the predetermined angular range (Δ) is at least 10°, and preferably lies at least in the range between 20° and 30°.

11. Method according to claim 1, characterised in that, various delivery quantities are regulated in such a way, that, for large delivery streams, the intake valve (5) is automatically driven during certain cycles and is driven with constantly variable backflow regulation during certain cycles; that, that, for middle-sized delivery quantities, the intake valve (5) is driven during every cycle with constantly variable backflow regulation; and that, for small delivery quantities, the intake valve (5) is constantly held open during certain cycles under skip regulation, and driven with constantly variable backflow regulation during certain cycles.

12. Reciprocating compressor with delivery quantity regulation, in particular with constantly variable delivery quantity regulation, with an unloader (6) arranged on at least one self-acting intake valve (5) of the compressor, with a control device (2) for driving the unloader (6), as well as with a closing body (5b) of the intake valve (5), wherein the unloader (6) acts on the closing body (5b) in such a way that the intake valve (5) is opened over a controllable part of the working stroke of the compressor, characterised in that, the control device (2) comprises a drive mechanism (2n) which acts via a connection means (7) on the unloader (6), wherein the control device (2) comprises a constantly variable backflow regulation, in which the unloader (6) lies against the closing body (5b) during a first section (K1) of the cycle of crank rotation and prevents its shutting, and in which the unloader (6) returns during a second section (K2) of the cycle of crank rotation such that the closing body (5b) shuts, and wherein the control device (2) preferably comprises a skip regulation, in which the unloader (6) prevents the shutting of the closing body (5b) during a complete cycle of crank rotation, and wherein the control device (2) is configured to steer drive mechanism (2n) and thereby the unloader (6) in such a way that the speed of the closing body (5b) is reduced prior to its seating on the intake valve (5), in order to seat the closing body (5b) gently on the intake valve (5).

13. Compressor according to claim 12, characterised in that, the control device (2) comprises a mechanism for measuring and/or calculating the pressure progression (P) in the compression space of the reciprocating compressor, and that the control device (2) is configured such that it drives the closing body (5b) via the unloader (6) in free-running mode or with backflow regulation or with skip regulation, in order to open the pressure valve (8) automatically during a total opening angle (Kv).

14. Compressor according to claim 12, characterised in that, the control device (2) comprises a displacement sensor (2h), which captures the displacement of the drive mechanism (2n) and/or of the unloader (6) and/or of the closing body (5b).

15. Compressor according to claim 12, characterised in that, the drive mechanism (2n) is in the form of an electromagnet (2a) with solenoid, with a movable magnet anchor (2b) and a fixedly arranged magnet core (2c) with magnet coil (2d), wherein the connection means (7) is fixedly connected with the magnet anchor (2b), and wherein the magnet anchor (2b) is mounted so as to be movable in the direction of extension of the connection rod (7).

16. Compressor according to claim 12, characterised in that, the drive mechanism (2n) comprises a steerable damping mechanism (2o), for damping the speed of the unloader (6).

17. Compressor according to claim 16, characterised in that the damping mechanism (2o) is electrically steerable, and that the damping mechanism (2o) comprises an electrorheological or magnetorheological liquid.