Piston Compressor

Abstract

A piston compressor comprising a housing (8) with a compression chamber (13) therein, the compression chamber (13) having an inlet, an outlet and a piston (10), the piston (10) being arranged in the compression chamber (13) so as to be movable back and forth in an axial direction (X-X') between a top dead center and a bottom dead center, the extent of which is determined by a kinematic mechanism (20) to which the piston (10) is connected, characterized in that the drive is formed exclusively by an electromagnetic linear drive (25) of the piston (10).

Description

[Technical Field]

[0001] The present invention relates to piston compressors, particularly but not exclusively to large capacity piston compressors of greater than 30 kW up to 600 kW or more capacity. [Background technology]

[0002] Such piston compressors are used for gas compression at very high operating pressures, for example 2000 kPa or more.

[0003] Traditionally, a piston compressor comprises a piston compressor element, which characteristically comprises a housing containing a compression chamber, a piston disposed within the compression chamber and movable axially back and forth between top and bottom dead centres by a drive shaft driven by a rotary motor, a kinematic mechanism in the form of a crank and rod mechanism within the housing between the drive shaft and the piston, and possibly an additional piston rod which moves linearly with the piston to form a link between the piston and the crank and rod mechanism.

[0004] To achieve such high gas pressures, a multi-stage piston compressor is usually used, comprising two or more of the above piston compressor elements, which are connected in series with each other via their gas inlets and gas outlets and mounted on a shared drive group in the form of a housing in which the shared drive shaft is supported together with a crank and rod mechanism connected to the piston compressor elements and optionally a piston rod connecting the piston to the crank and rod mechanism.

[0005] The drive group typically includes a rotary motor, typically an electric motor, driving a shared drive shaft, often via a belt drive. Such belt drives have the advantage of being relatively inexpensive, but also the disadvantage of incurring relatively large power losses, up to 3 to 5% of the motor's nominal capacity.

[0006] Needless to say, the drive group must be designed to handle the full power of the motor, and hence its full compression capacity, and therefore is relatively heavy and bulky for large capacity piston compressors.

[0007] In view of the large mechanical forces acting on the crank and rod mechanism, oil film bearings are generally used, which incur a power loss of between 5% and 10% and also require complex injection systems to supply the bearings with enough oil in all conditions.

[0008] Specially designed axial seals are used to prevent compressed gas from leaking into the drive group housing and out through the drive shaft, so the housing is not completely airtight sealed.

[0009] Also, conventionally, piston compressor applications are known, in which a piston moves back and forth by electromagnetic actuation to compress gas in a compression chamber. However, this application is limited to low capacities. High-capacity academic research results in very heavy and bulky compressors, for example with a 400 kg piston for a 30 kW capacity.

[0010] Furthermore, this application requires complex motion control with a wide safety margin to avoid collision between the piston head and the end wall of the compression chamber at the end of the compression stroke. In consideration of this wide safety margin, it is necessary that there is always sufficient play between the piston and the end wall of the compression chamber when top dead center is reached, which again leads to a smaller pressure rise than theoretically possible with a smaller safety margin and also to a lower capacity gain, thereby limiting the application field of piston compressors. Summary of the Invention [Problem to be solved by the invention]

[0011] SUMMARY OF THE INVENTION It is an object of the present invention to provide a solution to one or more of the above or other disadvantages. [Means for solving the problem]

[0012] To this end, the invention relates to a piston compressor comprising a housing with a compression chamber therein, the compression chamber having an inlet, an outlet and a piston, the piston being arranged in the compression chamber so as to be able to move axially back and forth between a top dead center and a bottom dead center, the range of which is determined by a kinematic mechanism to which the piston is connected, the drive being formed exclusively by an electromagnetic linear drive of the piston.

[0013] Since the piston or pistons are no longer driven by a conventional crank and rod mechanism, a rotary drive motor is no longer required and the drive group comprising the crank and rod mechanism can be implemented in a smaller, lighter and cheaper manner.

[0014] Furthermore, such piston compressors according to the present invention are more efficient due to the elimination of losses in the motor and belt drive, and because conventional "hydrodynamic bearings" can be replaced with more conventional, low-loss bearings, which do not require lubrication in contrast to sealed grease-lubricated bearings such as grease-lubricated roller bearings (i.e., bearings with rolling elements confined in a space between grease-filled inner and outer rings), although "mini" hydrodynamic bearings are still possible.

[0015] Because the kinematic mechanism ensures that there is no risk of hitting the end wall of the compression chamber at top dead center at the end of the compression stroke, a very small safety margin can be used and the piston can be very close to this wall with minimal head space between them, which is useful because the smaller the head space, the greater the upward pressure of the gas in the compression chamber, thereby broadening the range of applications for the compressor.

[0016] As a result, the piston compressor of the present invention also does not require complex controls to maintain a minimum headroom.

[0017] Any small deviations at the end of the compression stroke are absorbed by the kinematic mechanism, which does not allow the piston to travel beyond top dead center.

[0018] Preferably, the piston is driven at a frequency that closely matches the natural frequency of the piston compressor, in particular the natural frequency of the piston and the entire kinematic mechanism in combination with the air, mechanical or electromechanical spring, which allows for an energetically more efficient way of compressing the gas.

[0019] Preferably, the kinematic mechanism comprises a simple conventional crank and rod mechanism comprising a crank rotatable about a crankshaft perpendicular to the direction of linear motion of the piston, and a drive rod hinged at one end to the crank by a crankpin and at the other end to the piston by a piston pin, the crankshaft, crankpin and piston pin preferably being supported by sealed grease lubricated bearings.

[0020] Because the housing of a piston compressor does not have input and output shafts for driving the pistons and does not require external lubrication of the bearings, the housing can be completely sealed, with the exception of the gas inlet and outlet to and from the compression chamber.

[0021] The electromagnetic drive may comprise a direct electromagnetic drive that influences the piston via one or more electrical coils around the compression chamber.

[0022] Additionally or alternatively, the electromagnetic drive may comprise an indirect electromagnetic drive for a piston including a plunger, the plunger being coupled to the piston and moving synchronously back and forth therewith in a linear guide or housing extending parallel to the axial direction of the compression chamber, one or more coils arranged around the linear guide inductively interacting with each of the plungers.

[0023] The present invention also relates to a multi-stage piston compressor comprising at least two stages of compression chambers connected in series with each other by an inlet and an outlet, the pistons being movable back and forth by a linear electromagnetic drive, each piston being connected to its own kinematic mechanism.

[0024] In this case, if possible, at least two of the kinematic mechanisms are mechanically coupled to each other so that they move synchronously, and in the case of crank and rod mechanisms, the cranks of these at least two mechanisms are mounted on a shared crankshaft.

[0025] In order to better present the features of the present invention, some embodiments of a piston compressor will now be described in an exemplary and non-limiting manner with reference to the drawings. [Brief explanation of the drawings]

[0026] [Figure 1] 1 shows a schematic diagram of a conventional piston compressor. [Figure 2] 2 shows a graph of the forces acting on the piston compressor of FIG. 1 when in use. [Figure 3] 1 is a schematic diagram of a piston compressor according to the present invention; [Figure 4] 4 is a graph of the forces acting on the piston of the piston compressor of FIG. 3, shown together with the graph of FIG. 2 for comparison. [Figure 5] 3 shows another embodiment of a piston compressor according to the present invention. [Figure 6] 3 shows another variant of the multi-stage piston compressor according to the invention; [Figure 7] 3 shows another variant of the multi-stage piston compressor according to the invention; DETAILED DESCRIPTION OF THE INVENTION

[0027] FIG. 1 shows a piston compressor 1 including a drive group 2 and a piston compressor element 3 mounted thereon according to the prior art. The drive group 2 includes a housing 4 which rotatably supports a drive shaft 5 which is driven by an electric rotary motor 6 via a belt transmission 7 .

[0028] The piston compressor element 3 comprises a housing 8 mounted on the housing 4 of the drive group 2 and characterized by a cylinder casing 9 in which a piston 10 is arranged which is movable back and forth in an axial direction X-X' and which is further closed at one end by an end wall 11.

[0029] Between the piston top 12 of the piston compressor element 3, the end wall 11 and the cylinder barrel 9 is confined a compression chamber 13 which is connected in a known manner to the environment by a sealed inlet 14 with an intake valve 15 and a sealed outlet 16 with an exhaust valve 17 for drawing in gas for compression as shown by arrow I and for expelling the gas in the direction of arrow O at the end of the compression stroke.

[0030] During the compression stroke, the piston 10 moves from the so-called bottom dead center, which is the furthest point towards the end wall 11, to the so-called top dead center, which is the closest point towards the end wall 11, with the intake valve 15 and the exhaust valve 17 closed.

[0031] At the top dead center, the volume of the compression chamber 13 (so-called dead volume) is minimum, and the gas pressure in the compression chamber 13 at this point is high.

[0032] The piston rod 18 is connected to the piston 10, extends in the axial direction XX, and can move back and forth in synchronization with the piston 10 within a seal guide 19 of the housing, which forms a gas seal between the housing 8 of the piston compressor element 3 and the housing 4 of the drive group 2 to prevent compressed gas from leaking through the passages in the housing 4 of the drive group 2 and the drive shaft.

[0033] Between the piston rod 18 and the drive shaft 5 there is provided a kinematic mechanism 20 for converting the rotational movement of the drive shaft 5 into back and forth movement of the piston 10. In the case of Figure 1 this is a crank and rod mechanism, comprising a radially oriented crank 21 which rotates with the drive shaft 5, and a drive rod 22 which has one end attached to the crank 21 by a crank pin 23 and the other end attached to the piston 10 or piston rod 18 by a piston pin 24. The operation of a prior art piston compressor is simple as follows.

[0034] The drive shaft 5 is driven in one direction by a motor 6, causing the crank 21 to rotate and the piston 10 to move back and forth. On any intake stroke from top dead center to bottom dead center, gas is drawn into the compression chamber 13 through the inlet 14, while on any other opposite movement from bottom dead center to top dead center, the drawn gas is compressed with the intake valve 15 and exhaust valve 17 closed.

[0035] In operation, the piston rod 18 and piston pin 24 are subjected to a gas pressure Fg and a sinusoidal inertial force Fi in harmony as shown in FIG. 1, the instantaneous values ​​of which are shown in the graph of FIG. 2 as a function of the rotation angle A of the crank 21. The gas pressure Fg is obviously proportional to the required operating pressure of the piston compressor 1.

[0036] Also shown in this graph is the resulting force Fg+Fi, which is the sum of forces Fg and Fi acting on the piston rod 18 and piston pin 24. During the compression stroke of the piston 10, the piston rod 18 is compressed by the compression force.

[0037] Constructively, this resulting force may not be higher than a certain maximum value Frmax, which is determined primarily by the compressive strength of the piston rod 18 and / or the strength of the piston pin 24, and may often be a limiting factor in the design or selection of the piston compressor depending on the desired operating pressure, and the drive group must be selected to match a piston rod and piston pin that are strong enough to handle the desired gas pressure.

[0038] As shown schematically in FIG. 3, the piston compressor 1 of the present invention differs from the conventional piston compressor 1 of FIG. 1 in that in the present case there is no motor 6 for driving the piston 10 via the kinematic mechanism 20, instead the driving of the piston 10 is solely performed by an electromagnetic linear drive 25 of the piston 10. In this case, the piston is connected to the kinematic mechanism 20 directly, i.e. without the interposition of a piston rod.

[0039] The electromagnetic linear drive 25 consists of one or more electric coils 26 arranged around or along the cylinder chamber 13 and, when reinforced by a control device 27, applies an axial force Fe directly and inductively to the piston 10, which for this purpose may be made of a suitable magnetically inductive material or may have, for example, one or more permanent magnets (not shown).

[0040] In the case of FIG. 3, three coils 26 are provided which can be activated separately or together to apply a specific force curve to the piston 10 in order to move the piston back and forth in an appropriate manner, including the gas to be compressed in the compression chamber 13.

[0041] For this purpose, the piston compressor 1 is characteristically provided with means 28 for determining the current position of the piston 10, for example in the form of means for measuring the angle A of the crank 21 at a given point in time, which means are connected to the control device 27.

[0042] As shown in the graph of FIG. 4, as the crank 21 rotates, each coil 26 is separately activated to apply three electromagnetic forces Fe1, Fe2, and Fe3 to the piston 10 according to the measured angle A, and the force curves of these three forces Fe1, Fe2, and Fe3 can overlap each other in time to appropriately approximate the force graph Fg+Fi of FIG. 2, with the aim of generating resultant forces that ensure that the directions of the resultant forces are opposite at top dead center and bottom dead center.

[0043] The control program of the control device 27 does not need to be extremely accurate, since the kinematic mechanism 20 provides a limit to the back and forth movement of the piston 10 between bottom and top dead center, so that there is no risk of the piston 10 hitting the end wall 11 at the end of the compression stroke, even in the case of a slight deviation of the resulting force curve that would prevent the resulting force from changing direction when top or bottom dead center is reached.

[0044] Therefore, the design of the control device does not need to take into account a wide safety margin, and as a result, high pressures can be achieved by minimizing the dead volume between the piston 10 and the end wall 11 of the compression chamber 13.

[0045] The frequency of the piston's back and forth motion corresponds to the natural frequency of the piston compressor, in particular the natural frequency of the piston 10 and the entire kinematic mechanism 20 in combination with, for example, an air, mechanical or electromechanical spring formed by the compressed gas in the compression chamber 13, resulting in energy-efficient compression.

[0046] In the present invention, since there is no motor 6 and belt transmission 7, the kinematic mechanism 20 does not need to transmit force to drive the piston 10, and as a result, the kinematic mechanism 20 can be designed in a lighter and less robust manner, and the bearing and lubrication requirements of the kinematic mechanism 20 can be lower.

[0047] For the same reason, the interior space bounded by the housings 4 and 8 can be sealed by a piston. It is clear that the piston 10 may be coupled to the kinematic mechanism 20 by means of a piston rod 18 connected to the piston 10. Since the piston is not driven by the piston rod 18, the forces acting on it are much smaller than in conventional rotary motor driven piston compressors.

[0048] FIG. 5 shows a variant of the piston compressor 1 of the present invention, in which the piston 10 is a conventional piston without a coil 26 around the cylinder casing 9, but the electromagnetic drive 25 of the piston 10 is realized using an external plunger 29 which is arranged to be movable back and forth within a linear guide 30, around which one or more coils 26 can interact inductively with the respective plunger 29 when encouraged, in order to electromagnetically drive the piston 10 indirectly via a connecting rod 31 extending through the compression chamber 13 and said end wall 11.

[0049] It is clear that a combination of direct assistance of the piston 10 and indirect assistance by an internal or external plunger 29 is possible. Furthermore, the piston 10 and the plunger(s) 29 may be implemented by a linear motor, in particular a linear step motor.

[0050] FIG. 6 shows a four-stage multi-piston compressor 1 having four pistons 10 each electromagnetically driven in its own compression chamber 13, the compression chambers 13 being connected in series with one another at inlets 14 and outlets 16. In this case, each piston 10 is in its own sealed housing. 4、8 2. It is arranged with its own kinematic mechanism 20 within the In this case, the control device 27 is connected to four pistons 10 .

[0051] Figure 7 shows a shared sealed housing. 4、81 shows a multi-stage piston compressor 1 with two stages arranged within a housing, each having a piston 10 and its own kinematic mechanism 20, but the two kinematic mechanisms 20 are mechanically linked to each other, in this case each crank 21 being connected to the housing 4、8 The rotors are mounted on a shared crankshaft 32 supported on conventional ball bearings 33 within the rotor shaft.

[0052] The invention is not limited to the embodiments described above and shown in the drawings, but rather the piston compressor of the invention can be implemented in many different variants without departing from the concept of the invention.

Claims

1. A piston compressor including a housing (8) with a compression chamber (13) therein, the compression chamber (13) having an inlet, an outlet, and a piston (10), the piston (10) being arranged to be movable back and forth in an axial direction (X-X') between top dead center and bottom dead center within the compression chamber (13) defined by a kinematic mechanism (20) to which the piston (10) is coupled; the drive is formed exclusively by an electromagnetic linear drive (25) of said piston (10), the electromagnetic linear drive (25) comprises an electromagnetic drive for the piston (10) including a plunger (29), the plunger (29) being arranged to be movable back and forth within a linear guide (30) extending parallel to the axial direction (X-X') of the compression chamber (13), one or more coils (26) arranged around or along the linear guide (30) being capable of inductively interacting with the plunger (29); The plunger (29) is provided with one or more magnets; the one or more magnets are permanent magnets, the frequency of the back and forth movement of the piston (10) corresponds to the natural frequency of the piston compressor (1); The natural frequency of the piston compressor (1) is the natural frequency of the entire kinematic mechanism (20) combined with the piston (10) and an air spring, a mechanical spring, or an electromechanical spring. A piston compressor characterized by:

2. The electromagnetic linear drive (25) comprises an indirect electromagnetic drive for the piston (10), including a plunger (29); The guide (30) of the plunger (29) is arranged in the axial direction (X-X') of the compression chamber (13), The plunger (29) is rigidly and mechanically fixedly connected to the piston (10) and is disposed on a rod (31) that moves back and forth in synchronization with the linear movement of the piston (10).

2. The piston compressor of claim 1.

3. The kinematic mechanism (20) comprises a crank and rod mechanism comprising a crank (21) and a drive rod (22), the crank (21) being rotatable about a crankshaft (32) perpendicular to the direction of linear motion of the piston (10), the drive rod (22) being hinged at one end to the crank (21) by a crank pin (23) and at the other end to the piston (10) by a piston pin (24).

3. The piston compressor according to claim 1 or 2.

4. The piston (10) is connected to the crank and rod mechanism by a linear piston rod (18) that is connected to the piston (10) and moves back and forth in synchronism with the piston (10).

4. The piston compressor according to claim 3.

5. The piston compressor (1) characteristically comprises a control device (27) for operating the electromagnetic drive device (25) during the entire compression stroke of the piston (10) from the bottom dead center to the top dead center of the piston (10). A piston compressor according to any one of claims 1 to 4.

6. the control device (27) is configured to provide a total compression capacity according to a curve that corresponds primarily to a capacity curve provided to the piston (10) by virtual driving of the piston (10) via the kinematic mechanism (20) exclusively by the rotary motor (6); 6. The piston compressor according to claim 5.

7. The housing (4, 8) does not include an input or output shaft for driving the piston (10). A piston compressor according to any one of claims 1 to 6.

8. The kinematic mechanism (20) is a crank and rod mechanism with a crankshaft (32), a crank pin (23), and a piston pin (24) supported exclusively by enclosed roller bearings. A piston compressor according to any one of claims 1 to 7.

9. The housing (4, 8) of the piston compressor (1) having the compression chamber including the piston and the kinematic mechanism (20) therein is a sealed housing. A piston compressor according to any one of claims 1 to 8.

10. A multi-stage piston compressor (1) comprising at least two stages of compression chambers (13) connected in series with each other by an inlet (14) and an outlet (16), wherein the pistons (10) can be moved back and forth by a linear electromagnetic drive (25), each of said pistons (10) being connected to its own kinematic mechanism (20). A piston compressor according to any one of claims 1 to 9.

11. At least two of the kinematic mechanisms are mechanically coupled to each other so as to move synchronously with each other; 11. The piston compressor of claim 10.

12. When the kinematic mechanism (20) is a crank and rod mechanism, at least two of the cranks (21) of the kinematic mechanism (20) are arranged on a shared crankshaft (32).

12. The piston compressor of claim 11.

13. The piston compressor (1) has a maximum compression capacity greater than 30 kW. A piston compressor according to any one of claims 1 to 12.

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