阅读说明：本技术 线性电机压缩机的操作方法及线性电机压缩机 (Method for operating linear motor compressor and linear motor compressor ) 是由 A·L·瓦勒 于 2020-02-05 设计创作，主要内容包括：本发明涉及一种线性电机压缩机(1)的操作方法,该线性电机压缩机包括线性电机(14)、气缸(2)和具有活塞(3)的可线性移动的自由活塞装置(16)。该气缸(2)和该活塞(3)形成压缩室(5),该自由活塞装置(16)由该线性电机(14)直接驱动并沿行程位移(X)在上死点(X-(oTP))和下死点(X-(UTP))之间来回移动。流体从外部供应到该压缩室(5),并且供应的流体在该压缩室(5)中被压缩或膨胀并且随后被再次向外排出。至少一个状态变量(Z-(soll))被指定用于该线性电机压缩机(1),并且该线性电机压缩机(1)被致动使得该线性电机压缩机(1)具有指定预定状态变量(Z-(soll))。(The invention relates to a method for operating a linear motor compressor (1) comprising a linear motor (14), a cylinder (2) and a linearly movable free piston device (16) having a piston (3). The cylinder (2) and the piston (3) form a compression chamber (5), the free piston device (16) being directly driven by the linear motor (14) and being displaced (X) along the stroke at the top dead centre (X) oTP ) And bottom dead center (X) UTP ) To and from. The fluid being supplied from the outsideTo the compression chamber (5) and the supplied fluid is compressed or expanded in the compression chamber (5) and then discharged outward again. At least one state variable (Z) soll ) Is designated for the linear motor compressor (1) and the linear motor compressor (1) is actuated such that the linear motor compressor (1) has a designated predetermined state variable (Z) soll )。)

1. Method for operating a linear motor compressor (1)Comprising a linear motor (14), a cylinder (2) and a linearly movable free piston device (16) with a piston (3), wherein the cylinder (2) and the piston (3) form a compression chamber (5), wherein the free piston device (16) is directly driven by the linear motor (14) and is displaced (X) along a stroke in the upper dead center (X)_OTP) And bottom dead center (X)_UTP) Wherein fluid is supplied to the compression chamber (5) from the outside, wherein the supplied fluid is pressurized or expanded in the compression chamber (5) and then discharged outward again, wherein at least one state variable (Z) is preset for the linear motor compressor (1)_soll) And the linear motor compressor (1) is controlled such that the linear motor compressor (1) has a predetermined state variable (Z)_soll) Characterised in that the free piston device (16) is moved from the bottom dead center (X)_UTP) Starting at a predetermined state variable (ZS) during the compression phase (AB) up to the opening point (B) of the outlet valve (6) and subsequently during the discharge phase (BC) up to the closing point (C) of the outlet valve (6)_oll) I.e. the predetermined speed-displacement curve, is driven such that the average speed (V) during the compression phase (AB)_m1) Above the average speed (V) during the discharge phase (BC)_m2)。

2. Method according to claim 1, characterized in that the free piston device (16) is moved from the top dead center (X)_OTP) Starting with a predetermined state variable (Z) during an expansion phase (CD) up to an opening point (D) of the inlet valve (7) and subsequently during an intake phase (DA) up to a closing point (A) of the inlet valve (7)_soll) I.e. the predetermined velocity-displacement curve, is driven such that the average velocity (V) during the expansion phase (CD)_m3) Above the average speed (V) during the suction phase (DA)_m4)。

3. Method according to any one of the preceding claims, characterized in that the speed of the free piston device (16) in the region of the opening point (B) of the discharge valve (6) is reduced to below the average speed (V) during the compression phase (AB)_m1)。

4. Root of herbaceous plantMethod according to any one of the preceding claims, characterized in that the velocity of the free piston device (16) in the region of the opening point (D) of the inlet valve (7) is reduced below the average velocity (V) during the expansion phase (CD)_m3)。

5. Method according to claim 3 or 4, characterized in that the free piston device (16) is accelerated again after the opening point (B) of the discharge valve (6) and/or the free piston device (16) is accelerated again after the opening point (D) of the inlet valve (7).

6. Method according to any one of the preceding claims, characterized in that the free piston device (16) is first directed towards the end of stroke, towards the bottom dead centre (X)_UTP) Is braked with a greater negative acceleration and subsequently braked with a lesser negative acceleration, wherein the free piston device (16) is at dead center (X)_UTPAnd) braking with less negative acceleration until it stops.

7. Method according to any one of the preceding claims, characterized in that the free piston device (16) is first directed towards the end of stroke, towards the top dead centre (X)_OTP) Is braked with a greater negative acceleration and subsequently with a smaller negative acceleration, the free piston device (16) being at top dead centre (X)_OTP) Is braked with a small negative acceleration until it stops.

8. Method according to any one of the preceding claims, characterized in that the travel displacement point (X)₁) And the set speed (V) of the free piston device (16) associated with it_soll) Is preset as a state variable (Z)_soll)。

9. Method according to any one of the preceding claims, characterized in that the displacement (X) is displaced along at least a partial section of the stroke (X) and preferably along the entire stroke (X)_L) Maintained set curve (S)_soll) Is preset as a state variable (Z)_soll)。

10. Method according to claim 9, characterized in that the displacement (X) is performed over the entire stroke_L) Required travel time (T)_L) Set curve (S) held during the period_soll) Is preset as a state variable (Z)_soll)。

11. Method according to any of the preceding claims, characterized in that the linear motor compressor (1) comprises a first and a second compression chamber (5a, 5b) operated in opposite directions by the free piston device (16).

12. Method according to any one of the preceding claims, characterized in that the bottom dead center (X)_UTP) And the top dead center (X)_OTP) And/or the top dead center (X)_OTP) And bottom dead center (X)_UTP) The velocity-displacement curve between is preset as the state variable (Z)_soll) The free piston device (16) moves back and forth according to the curve.

13. Method according to any one of the preceding claims, characterized in that the free piston device (16) is moved from the bottom dead center (X)_UTP) The displacement to the opening point (B) of the outlet valve (6) is started during the compression phase (AB) with a predetermined speed-displacement curve, so that the linear motor (14) must output a constant or substantially constant power in relation to time.

14. Method according to any of the preceding claims, characterized in that the predetermined state variable (Z) is compared to the rest of the velocity-displacement curve_soll) I.e. the predetermined speed-displacement curve is in the range of at least one of the following points:

-the opening point (B) of the discharge valve (6),

-the closing point (C) of the discharge valve (6),

-the opening point (D) of the inlet valve (7),

-the closing point (A) of the inlet valve (7),

has a lower speed so that the outlet or inlet valve (6, 7) moves at a lower speed.

15. Method according to any one of the preceding claims, characterized in that the linear motor (14) applies to the free-piston device (16) towards the bottom dead centre (X) during the entire expansion phase (CD), preferably during the expansion phase (CD) and the suction phase (DA)_UTP) The positive force acting.

16. Method according to any of the preceding claims, characterized in that the maximum stroke (X) of the linear motor (14) is varied_L) Or the top dead center (X)_OTP) And/or the bottom dead center (X)_UTP) To vary the volume delivered by the linear motor compressor (1).

17. Method according to any one of the preceding claims, characterized in that at the top dead center (X)_OTP) And the bottom dead center (X)_UTP) By operating the linear motor (14) as a generator to at least partially brake the free-piston device (16) during the reciprocating movement therebetween.

18. Method according to any of the preceding claims, characterized in that the linear motor (14) is operated as a generator by supplying pressurized fluid to the compression chamber (5) via the outlet valve (6), expanding the fluid in the compression chamber (5) and subsequently discharging it through the inlet valve (7), and that the free piston device (16) in the linear motor (14) operated as a generator is moved back and forth with a predetermined speed-displacement curve.

19. Linear motor compressor (1) comprising at least one linear motor (14), a cylinder (2) and a linearly movable free piston device (16) with at least one piston (3), the cylinder (2) and the piston (3) forming at least one compression chamber (5), the free piston device (16) being directly driven by the linear motor (14), the compression chamber (5) being in fluid-conducting communication with the outside through an outlet valve (6) and an inlet valve (7),a control device (20) controls the linear motor (14) such that the free-piston device (16) assumes a predetermined state variable (Z)_soll) At top dead center (X)_OTP) And bottom dead center (X)_UTP) To and from, characterized in that the actuation device (20) moves from the bottom dead center (X)_UTP) Controlling the free piston device (16) with a predetermined speed-displacement curve starting during the compression phase (AB) up to the opening point (B) of the outlet valve (6) and subsequently during the discharge phase (BC) up to the closing point (C) of the discharge valve (6), such that the average speed (V) during the compression phase (AB) is_m1) Higher than the average speed (V) during the discharge phase (BC)_m2)。

20. Linear motor compressor (1) according to claim 19, characterized in that the linear motor (14) is operable as a motor and as a generator and in that the drive means (20) drives the linear motor (14) such that when the free piston device (16) is at top dead center (X)_OTP) And bottom dead center (X)_UTP) Is driven with a predetermined speed-displacement curve.

Linear motor compressor (1) according to any one of claims 19 and 20, characterized in that the control device (20) is designed to be at the top dead center (X) along the stroke displacement (X), both in the part as generator and in the part as motor_oTP) And the bottom dead center (X)_UTP) The control device (20) comprises an energy store for temporarily storing the electrical energy obtained by the generator.

Technical Field

The present invention relates to a method of operating a linear motor compressor. The invention also relates to a linear motor compressor.

Background

It is known to compress gas by means of a linear motor compressor. Document US2018/0051690a1 discloses a free piston linear motor compressor, wherein the compressor is designed as a reciprocating piston compressor, whereby the linear motor is designed with two poles, whereby the whole free piston linear motor compressor operates at a resonance frequency. Such linear motor compressors are used for compressing gaseous process fluids, in particular natural gas. Such linear motor compressors operate continuously at a sinusoidal resonant frequency during the filling of natural gas cars. The operating possibilities of such linear motor compressors are extremely limited and economically disadvantageous.

Disclosure of Invention

The object of the invention is to operate a linear motor compressor for compressing and/or expanding a gaseous process fluid with a more advantageous operating method. Furthermore, the object of the invention is to design a more economically advantageous linear motor compressor for compressing and/or expanding gaseous process fluids.

This object is achieved by a method having the features of claim 1. The dependent claims 2 to 18 relate to further advantageous method steps. This object is further achieved by a linear motor compressor having the features of claim 19. Dependent claims 20 and 21 relate to further advantageous embodiments.

The object is in particular solved by an operating method for a linear motor compressor comprising a linear motor, a cylinder and a linearly movable free piston device with a piston, wherein the cylinder and the piston form a compression chamber, wherein the free piston device is directly driven by the linear motor and moves back and forth along a stroke displacement between a top dead center and a bottom dead center, wherein a fluid is supplied from the outside to the compression chamber, wherein the supplied fluid is compressed or expanded in the compression chamber and then discharged to the outside again, wherein at least one state variable is predetermined for the linear motor compressor, and wherein the linear motor is controlled such that the linear motor compressor has the predetermined state variable.

The object is further achieved, in particular, by a linear motor compressor comprising at least one linear motor, a cylinder and a linearly movable free piston device having at least one piston, wherein the cylinder and the piston form at least one compression chamber, wherein the free piston device is directly driven by the linear motor, wherein the compression chamber is in fluid-conducting communication with the outside via an outlet valve and an inlet valve, wherein a control device controls the linear motor such that the free piston device is moved back and forth between a top dead center and a bottom dead center with a predetermined state variable.

Preferably, at least one point of travel displacement or at least one time of travel displacement along the travel and the set speed or set acceleration or set force assigned to it are specified as state variables. Preferably, the relationship between the stroke displacement of the free piston device and its speed is specified as a predetermined state variable, hereinafter also referred to as speed-displacement curve. The velocity-displacement curve may comprise at least one point, a travel displacement and a predetermined associated velocity, and preferably comprises a plurality of points, each point comprising a location along the travel displacement and a velocity associated with that location.

Advantageously, a displacement setting curve, i.e. a setting curve relating to the stroke displacement and the set speed, the set acceleration and/or the set force, which is maintained along at least a partial section of the entire stroke displacement and preferably along the entire stroke displacement, is specified as the state variable.

Advantageously, a time-setting curve, i.e. a time-dependent setting curve with respect to the set speed, the set acceleration and/or the set force, is specified as the state variable, which travel time is to be maintained during a partial duration or a partial section of the entire travel, which travel time is preferably the travel time required during the entire travel.

In order to achieve the predetermined state variables during operation of the linear motor compressor, the linear motor compressor is advantageously operated in a control strategy, wherein the free piston device can be moved "free" on the basis of the forces acting in the compression chamber and, if necessary, additionally frictional forces, whereby the linear motor can exert a controllable force on the free piston device and thereby influence the free movement of the free piston device from the outside and preferably in a predetermined manner. Preferably, the linear motor is assigned a speed profile or a force profile with a displacement dependency or a time dependency, respectively, whereby the force profile can be modified by a control intervention during operation of the linear motor compressor to ensure that the free-piston device has a predetermined state variable or that the behavior of the free-piston device approaches the predetermined state variable as a result of the control intervention.

In an advantageous control strategy, the path-time dependence of the movement of the free-piston device and the path-time dependence of the piston movement are not directly controlled, i.e. a predetermined path-time curve for the movement of the free-piston device is not specified, but the movement curve of the free-piston device or the piston is the result of the force curve or of the force used. In this embodiment, the specified state variable is thus ultimately realized by specifying a force curve. The force curve used is particularly suitable for the respective application and the respective operating method of the linear motor compressor. As an application, the linear motor compressor can be operated, for example, as a compressor or as an expander of a gas. Preferably, the linear motor compressor is operated to compress gas. In an application as a compressor, the operating method or force profile can be optimized, for example, during a compression phase of the gas the free-piston device moves relatively fast, in particular at a higher average speed, and during a subsequent discharge phase of the gas the free-piston device moves at a reduced speed, in particular at a lower average speed, which reduces the flow resistance when the gas flows out of the compression chamber. Thus, for example, the time of a complete compression cycle can be kept constant, but by running faster through the compression phase and slower through the discharge phase, the flow resistance of the gas can be reduced during discharge, thereby also reducing the energy required to discharge the gas out of the compression chamber.

Due to the predetermined state variables, the free piston device and the entire linear motor compressor can be operated in various ways, depending on the desired variable to be optimized. In addition to the examples already described, the state variables can be selected, for example, in such a way that the maximum force to be transmitted by the linear motor or the maximum power to be transmitted by the linear motor is limited, or the energy required for operating the linear motor compressor is reduced by extracting energy from the linear motor in sections during a cycle and supplying it again with a delay. The method according to the invention therefore has the advantage that the linear motor compressor can be operated with a large number of possible predetermined state variables. The pistons of the reciprocating piston compressors known from the prior art are driven by a piston drive via a crosshead, which has the disadvantage that the movement of the piston is rigidly linked to the speed of the crankshaft and that the speed of the piston is determined in relation to the crankshaft rotation angle, in particular also by the geometric arrangement of the crankshaft and the crosshead. In contrast, the linear motor compressor according to the invention can be operated in a number of ways, in particular independently of the movement sequence determined by the crankshaft by a corresponding specification of a state variable (for example a set speed, a set acceleration or a set force associated with a stroke according to the present specification). Furthermore, the method of operation may be optimized for variables such as energy consumption, maximum linear motor power or maximum linear motor force, depending on requirements.

The linear motor compressor may include a single compression chamber. Particularly advantageously, the linear motor compressor comprises two compression chambers, namely a first and a second compression chamber. The free piston device preferably has a piston on each of two end faces spaced apart in the stroke direction, which pistons are operated by the free piston device in opposite directions so as to alternately compress and then discharge the fluid in one compression chamber, for example, in the first compression chamber, and simultaneously expand and suck the fluid in the other compression chamber, for example, in the second compression chamber, and vice versa.

The linear motor or free piston device particularly preferably has a stroke length in the range between 50 millimeters (mm) and 500 mm. The linear motor has at least three actively controllable magnetic poles arranged in succession in the direction of travel, and preferably has 5 to 50 actively controllable magnetic poles, and particularly advantageously 10 to 20 controllable magnetic poles. An advantage resulting from this number of actively controllable magnetic poles is that the force exerted by the linear motor on the free piston device during movement along the stroke displacement can be controlled in relation to the stroke displacement or in relation to time by a corresponding selective activation of the magnetic poles connected individually or in groups. In an advantageous method of operation, only positive electrical power is supplied to the linear motor to thereby drive the free piston device. In a further advantageous operating method, electrical power is dissipated from the linear motor along at least a partial section of the entire stroke travel, so that the linear motor generates a braking action in this partial section, so that the free piston device is braked by the linear motor. Advantageously, the braking effect or the braking power output can also be controlled in dependence on the distance travelled. The linear motor can thus be operated in a driving mode only, or in a driving and braking mode, or in a combination of at least two of driving, braking and neutral, neutral being understood to mean that the linear motor affects neither driving force nor braking force. In a particularly advantageous operating method, the electrical energy consumed by the linear motor is temporarily stored in a battery and subsequently fed back to the linear motor with a delay. This enables the linear motor compressor according to the invention to be operated particularly energy-efficient. The linear motor compressor is preferably operated at a speed of 200 to 1000 revolutions per minute or at a stroke frequency of 200 to 1000 cycles or reciprocations per minute.

The movement cycle of the free piston device is a complete movement cycle once from the starting point through the top dead center and the bottom dead center of the piston movement. The cycle of piston movement comprises a compression phase of movement from bottom dead centre to top dead centre in the compression chamber, followed by a discharge phase, then an expansion phase of movement from top dead centre to bottom dead centre in the compression chamber, followed by a suction phase for the fluid to be delivered. The starting point is basically arbitrary. For example, the starting point is the bottom dead center.

The free piston device preferably moves back and forth between the top dead center and the bottom dead center with a predetermined speed-displacement curve.

Preferably, the free piston device moves from the bottom dead center to the opening point of the discharge valve during the compression phase according to a predetermined speed-displacement curve, so that the linear motor has to deliver a constant or substantially constant power. This has the advantage that no high and possibly unpredictable current peaks occur during the supply of the linear motor.

Preferably, the free-piston device is driven from bottom dead center to an opening point of the discharge valve during the compression phase and then to a closing point of the discharge valve during the discharge phase according to a predetermined speed-displacement curve, such that the average speed is higher during the compression phase than during the discharge phase and/or such that the average speed is higher during the expansion phase than during the suction phase.

In an advantageous method, the predetermined speed-displacement curve or the predetermined speed-time curve of the free-piston device has a reduced speed at least in the region of one of the following switching points: the opening of the discharge valve, the closing of the discharge valve, the opening of the inlet valve and the closing of the inlet valve, and having a reduced velocity compared to the rest of the velocity-displacement curve, such that the discharge valve or the inlet valve of the free-piston device, which opens or closes at a reduced velocity, moves at a reduced velocity. The reduced speed of opening or closing the valve preferably results in reduced wear of the valve, which advantageously results in an increased service life or service life of the valve.

In an advantageous method, the compression chamber has an expansion phase between a closing point of the outlet valve and an opening point of the inlet valve, wherein the linear motor is controlled such that it actively drives the free piston device throughout the expansion phase.

In an advantageous method, the volume delivered by the linear motor compressor is changed by changing the maximum stroke of the linear motor or the position of the top dead center and/or the bottom dead center, so that the delivered volume can be changed in the short term or also in the long term, for example by reducing or increasing it.

In an advantageous method, the free-piston device is at least partially braked during the reciprocating movement between the upper dead center and the lower dead center by operating the linear electric machine as a generator. This makes it possible to reduce the speed of the free piston device particularly quickly. Preferably, the released braking energy is converted into electrical energy and temporarily stored for later use.

In an advantageous method, the linearly displaceable piston mechanism is operated as an expander for the fluid, and the linear motor is thereby operated as a generator at least during a partial section of the movement in the stroke direction X, because the compression chamber of the linear motor compressor now serves as an expansion chamber, because pressurized fluid is supplied to the expansion chamber via the outlet valve, the fluid expands in the compression chamber operating as an expansion chamber and is subsequently discharged via the inlet valve, and because the free piston device of the linear motor operating as a generator is displaced back and forth at a predetermined speed-distance curve or a predetermined speed-time curve. In an advantageous procedure, the opening and closing of the outlet valve and/or the inlet valve is actively controlled in dependence on the position of the free-piston device.

Advantageously, the linear motor compressor comprises at least one linear motor, a cylinder and a linearly movable free piston device with at least one piston, the cylinder and the piston forming at least one compression chamber, the free piston device being directly driven by the piston, the compression chamber being in fluid conducting communication with the outside via an outlet valve and an inlet valve, the control device controlling the linear motor such that the free piston device is moved back and forth preferably with a predetermined motor and/or generator power curve between top dead center and bottom dead center.

Advantageously, the linear motor compressor comprises a first and a second compression chamber, which are arranged in opposite directions with respect to the free piston device, so that they act in opposite directions.

Advantageously, the linear motor of the linear motor compressor may be used as a motor and/or as a generator, wherein the control means controls the linear motor such that the free piston means has a predetermined speed-displacement curve or a predetermined speed-time curve during movement between top dead center and bottom dead center.

The linear motor comprises at least three pole pairs, preferably 5 to 50 pole pairs, distributed or spaced apart from each other in the longitudinal direction of the linear motor.

Linear motor compressor comprising at least one linear motor, a cylinder and a linearly movable free piston device with at least one piston, wherein the cylinder and the piston form at least one compression chamber, wherein the free piston device is directly driven by the linear motor, the compression chamber is in fluid-conducting communication with the outside via an outlet valve and an inlet valve, a control device controls the linear motor such that the free piston device assumes a predetermined state variable Z_sollMoving back and forth between the top dead center and the bottom dead center.

In a preferred embodiment, the linear motor compressor according to the present invention is advantageous in that it has no moving parts other than the valve and free piston device, which improves the lifespan and efficiency of the linear motor compressor, and also reduces manufacturing costs, installation and maintenance costs. Furthermore, the linear motor compressor is preferably designed oil-free, which means that no oil is required for lubrication. The linear motor compressor according to the invention is particularly suitable for compressing gases such as natural gas, other hydrocarbons, hydrogen or air. However, the linear motor compressor according to the invention is also suitable for expanding pressurized gas, whereby the linear motor may at least temporarily be operated as a generator, in particular during expansion. Further, the linear motor compressor according to the present invention is also adapted to simultaneously compress gas and expanded gas by expanding the gas in one chamber of the linear motor compressor and simultaneously compressing the gas in the other chamber of the linear motor compressor.

The combination of the linear motor with the free piston compressor allows to build a compact linear motor compressor. Static and dynamic behavior are linked due to the direct mechanical connection of the two systems. Therefore, good performance and high efficiency of the linear motor compressor can be preferably achieved if the compressor and the linear motor are designed to work optimally in cooperation and preferably to operate in the resonance frequency range. Preferably, the free piston compressor can fully exploit its advantages under such operating conditions. In addition to a compact design, there is also the advantage that the piston can be hermetically sealed from the outside in a relatively simple manner and therefore at low cost, since the two cylinders in which the two pistons are located can be designed to be sealed from the outside in a low-cost, gas-tight manner, which makes it possible to compress gas under high demands on environmental conditions, since there is little or no leakage of the gas pumped at the linear motor compressor. Advantageously, the two cylinders and the stator of the linear motor form a hermetic enclosure. Furthermore, a crank mechanism like a conventional piston compressor is not required. This eliminates the need for lubricated parts that have mechanical energy conversion losses. The ability to dispense with lubricant also makes the linear motor compressor according to the invention suitable for applications with high cleanliness requirements.

Drawings

The invention is explained in more detail below with reference to advantageous embodiments and the accompanying drawings, in which:

figure 1 schematically illustrates a linear motor compressor and associated pressure-volume diagram;

figure 2 is a schematic longitudinal section of another double acting linear motor compressor;

fig. 3 schematically shows a longitudinal sectional view along an intersection line F-F through the linear motor of the linear motor compressor according to fig. 2;

fig. 4 schematically shows a cross-section along an intersection E-E through the linear motor of the linear motor compressor according to fig. 3;

FIG. 5 is four simplified diagrams of a method of operating an idling linear motor compressor showing time-dependent stroke, speed, acceleration and motor force;

FIG. 6 is four schematic diagrams of another method of operation of an idling linear motor compressor showing time-dependent stroke, speed, acceleration and motor force;

fig. 7 is a velocity-displacement diagram of two pistons of the linear motor compressor according to fig. 2 according to a first method of operation;

FIG. 8 is a velocity-distance diagram according to a second method of operation;

FIG. 9 is a velocity-distance diagram according to a third method of operation;

FIG. 9a is a detailed aspect of a third method of operation;

FIG. 9b is another detailed aspect of the third method of operation;

fig. 10 is a driving apparatus for the linear motor compressor according to fig. 2.

In principle, identical components in the figures are provided with the same reference numerals.

Detailed Description

Figure 1 schematically shows a linear motor compressor 1 comprising a linear motor 14 and a double acting reciprocating piston compressor 15. The reciprocating piston compressor 15 comprises a cylinder 2 in which a linearly movable piston 3 is arranged, which is directly connected to a linear motor 14 by a piston rod 9 and is directly driven by the electric linear motor. Direct connection or direct drive is understood here to mean that no transmission is provided between the piston 3 and the linear motor 14, so that the force is transmitted directly between the linear motor 14 and the piston 3 and therefore without any intermediate transmission. In a possible embodiment, a flexible joint may also be provided between the piston 3 and the linear motor 14, which preferably allows independent alignment of the piston 3 and the linear motor 14. The cylinder interior 5 is divided by the piston 3 into a first compression chamber 5a and a second compression chamber 5b, wherein the first and second compression chambers 5a, 5b, due to the geometric arrangement, operate in opposite directions during operation. The first and second compression chambers 5a, 5b are each connected in fluid communication to an external space outside the cylinder interior 5 via inlet valves 7a, 7b and outlet valves 6a, 6 b. Typically, the fluid lines are arranged downstream of the valves 6a, 6b, 7a, 7b, as shown in fig. 1, which deliver fluid to downstream devices or supply it upstream of upstream devices. The piston 3 can assume a plurality of possible piston positions during operation of the cylinder interior 5, three exemplary positions of the piston 3 being shown in fig. 1, at the bottom dead center X_UTPAt a first piston position 3a, at top dead center X_OPTA second piston position 3c and a third piston position 3B, wherein the third piston position 3B corresponds to a position in which the discharge valve 6a is ideally open at the opening point B. Bottom dead center X_UTPFirst piston position 3a, top dead center X_OPTSecond piston position 3c and top dead centre X_OPTIn the third piston position 3 b. Due to the friction, the outlet valve 6a normally opens slightly later than the pressure Pa shown in fig. 1 or at a slightly higher pressure, i.e. in the region of the opening point B shown。

Above the reciprocating piston compressor 15, a related idealized P-V diagram, also called pressure-volume diagram, is shown, which shows the pressure P of the gas compressed by the reciprocating piston compressor 15 in the first compression chamber 5a in relation to the volume of the first compression chamber 5 a. The first compression chamber 5a has a stroke volume VH, a suction volume VS, and a dead volume Vtot, and the volume V increases rightward. The figure also shows that the pressure P of the gas in the first compression chamber 5a is related to the stroke X of the piston 3, wherein the stroke X in the figure shown increases positively to the left, so that the positive direction of the stroke X is to the left. Fig. 1 shows the piston 3 in a first piston position 3a, in which the piston 3 is in the bottom dead center X_UTPWhereby the gas in the first compression chamber 5a has the suction pressure Ps. The curves of the idealized p-V diagram are briefly described below. From bottom dead centre X_UTPInitially, the piston 3 is moved in the positive direction X, whereby the inlet valve 7a is automatically closed at the closing point a, ideally due to the pressure increase in the first compression chamber 5a, and during the compression phase BA the gas in the first compression chamber 5a is compressed to the outlet pressure Pa, whereby the outlet valve 6a is automatically opened at the opening point B, ideally at the outlet pressure Pa. During the subsequent exhaust phase BC, the piston 3 is directed towards the top dead centre X_OTPMoves so that the gas located in the first compression chamber 5a is discharged through the outlet valve 6a until the piston 3 reaches the top dead center X_OTPAnd ideally closes the outlet valve 6a at closing point C. During the subsequent expansion phase CD, the piston 3 is facing the bottom dead center X_UTPThe residual gas, which is still in the first compression chamber 5a, is displaced and expanded to the suction pressure Ps, so that the inlet valve 7a is ideally automatically opened at the opening point D. During the subsequent suction phase DA, gas is sucked into the first compression chamber 5a via the inlet valve 7a until the piston 3 has reached the bottom dead center X_UTPAnd the inlet valve 7a is ideally closed at closing point a. The term "idealized" in relation to points A, B, C and D means that these points are not exactly located at the positions shown in FIG. 1 in actual operation, such as by the effect of the existing friction of the valve, but rather are within a close proximity of the points.

The process shown in fig. 1, which occurs between point A, B, C and point D, is repeated during operation of the reciprocating piston compressor 15. The same process also runs in the opposite direction in the second compression chamber 5b, so that the second compression chamber 5b is in the expansion phase or suction phase and the first compression chamber 5a is in the compression phase or discharge phase, and vice versa.

In a particularly advantageous embodiment, the inlet valves 7a, 7b and the outlet valves 6a, 6b are opened and closed automatically. However, it may also prove advantageous to open and/or close the inlet valves 7a, 7b and/or the outlet valves 6a, 6b in a controlled manner. This is particularly necessary when the linear motor compressor 1 is expanding gas at pressure Pa by reversing the cycle shown in fig. 1 (i.e. by controlled opening of the discharge valve 6a back to a along points A, D, C and B), and the gas enters and expands the first compression chamber 5a at pressure Pa to move the piston 3 along line CB until at point B the discharge valve 6 closes and the gas present in the first compression chamber 5a expands along line BA until the piston 3 reaches a lower low point X_UTPAccordingly, the inlet valve 7a at the point a is controllably opened. The piston 3 then moves along the line AD, the gas is discharged from the first compression chamber 5a and the inlet valve 7a is controllably closed at point D. The residual gas located in the first compression chamber 5a is compressed along the line DC to a pressure Pa and the outlet valve 6 is opened in a controlled manner at point C so that the gas flows again into the first compression chamber 5a at the pressure Pa. Particularly advantageously, the above cycle is operated in the direction of the succession of points A, D, C and B with a double-acting reciprocating piston compressor 15 comprising a first and a second compression chamber 5a, 5B as shown in fig. 1. The cyclic process in the direction of the continuation points A, D, C and B has the advantage that the linear electric machine 14 can be operated as a linear generator, so that the mechanical energy can be converted into electrical energy by the described gas expansion. In another advantageous embodiment, the linear motor compressor 1 can therefore be operated as desired to compress or expand fluid, or in a mixed mode with intermittent compression and bidirectional expansion, whereby electric energy is supplied to the linear motor or consumed, depending on the operating mode. In a further advantageous embodiment, the linear motor compressor 1 can also be operated such that the fluid is compressed in the first compression chamber 5a and the fluid is expanded in the second compression chamber 5b, respectively, so that the first compression chamber isThe expansion energy released in 5a can be used to compress the fluid in the second compression chamber 5 b.

The linear motor compressor 1 can also be operated in reverse, compressing fluid in the first compression chamber 5a and expanding it in the second compression chamber 5b as required for compression or expansion. Depending on the operating mode, the linear motor 15 may be powered or discharged, or may run idle without being powered.

In another possible embodiment of the reciprocating piston compressor 15, the second compression chamber 5b may be omitted, so that the reciprocating piston compressor 15 has only the first compression chamber 5a and no second compression chamber 5b that can run in the opposite direction.

Fig. 2 to 4 show another embodiment of the linear motor compressor 1. The linear motor compressor 1 comprises a free piston device 16 comprising a linear motor rotor 10 and a first piston 3 and a second piston 4. The stator 8 together with the linear motor rotor 10 forms a linear permanent magnet synchronous motor 14. The linear motor compressor 1 comprises a cylinder 2 with two cylinder chambers 5, wherein a first compression chamber 5a is formed by the first cylinder 2a and the first piston 3, and wherein a second compression chamber 5b is formed by the second cylinder 2b and the second piston 4. The first compression chamber 5a is in fluid communication with the outside through a first discharge valve 6a and a first inlet valve 7 a. The second compression chamber 5b communicates with the outside via a second discharge valve 6b and a second inlet valve 7b that transmits fluid. The first and second compression chambers 5a, 5b are operated in opposite directions by the free piston device 16. Preferably, sealing rings and/or bearing rings are also provided on the first and second pistons 3, 4 for supporting the free piston arrangement 16 within the linear motor compressor 1 and for sealing the pistons 3, 4 with respect to the compression chambers 5a, 5b, which rings are well known and not shown in fig. 2. The pistons 3, 4 can also be designed as labyrinth pistons, so that the sealing rings can be dispensed with, since the labyrinth structure on the surface of the pistons 3, 4 provides the sealing function. Fig. 3 shows a longitudinal section along the intersection line F-F of a linear permanent magnet synchronous motor 14, which motor 14 comprises a stator 8 with stacked stator segments 8a, comprises a plurality of preferably individually controllable stator windings 12a, 12b, 12c, 12d, 12e, 12F for generating actively controllable poles 13a-13F of respective magnetic fields, respectively, and comprises a linear motor rotor 10, which linear motor rotor 10 has a plurality of permanent magnets 10a spaced apart longitudinally from each other, which linear motor rotor 10 forms part of a piston rod 9. The piston rod 9 comprises a fastening section 9a, to which fastening section 9a the first piston 3 and the second piston 4 are connected, respectively. Furthermore, the linear permanent magnet synchronous motor 14 advantageously comprises two radial bearings 11 for guiding the piston rod 9.

Fig. 4 shows a section through the linear permanent magnet synchronous motor 14 along section line E-E, through the stator segment 8 and the second stator winding 12b, and through the piston rod 9 and the permanent magnet 10 a.

For example, a permanent magnet motor, an asynchronous motor or a reluctance motor is also suitable as the linear motor 14. The linear motor 14 and therefore also the slave pistons 3, 4 advantageously have a maximum stroke X in the range between 50 millimeters (mm) and 500mm_L. The linear motor 14 thus allows a relatively long stroke displacement.

The linear motor 14 shown in fig. 2 to 4 comprises six actively controllable poles 13a-13f, each pole being surrounded by a stator winding 12a-12f, preferably each stator winding 12a-12f being individually controllable. The linear motor 14 preferably has 3 to 10 actively controllable magnetic poles 13a-13f, or preferably 10 to 50 actively controllable magnetic poles 13a-13 f. The number of actively controllable magnetic poles 13a-13f depends inter alia on the maximum stroke X_LLength of (d). The number of actively controllable magnetic poles 13a-13f may also influence how precisely the force applied by the stator 8 to the rotor 10 of the linear motor, which force is time-dependent or dependent on the stroke X, is controlled.

Fig. 5 shows exemplary characteristic curves 30 to 33 of a possible control of the linear electric motor 14 as shown in fig. 1 or fig. 2, wherein the characteristic curves shown show the case in which the linear electric motor 14 is not connected to the reciprocating piston compressor 15, but only operates separately and independently of the reciprocating piston compressor 15. Characteristic curve 30 shows the curve at bottom dead center X_UTPTo the upper dead point X_OTPAnd back the stroke X of the linear motor 14 in relation to the time t during the complete cycle. Characteristic curve 31 shows the speed of the linear motor rotor 10 as a function of time t, the linear motor 14 being controlled such that the speed of the linear motor rotor 10 is dependent on time tThe time dependence increases linearly in section 31a and is constant in section 31b, decreases linearly in section 13c, and is zero in section 13d, so that the linear motor rotor 10 is stopped. When the linear motor rotor 10 stops, it has reached the top dead center X, as can be seen from the characteristic curve 30_OTP. At the return of movement to the bottom dead center X_UTPIn the course of (1), the speed of the linear motor rotor 10 increases linearly in a negative number in the section 31e, is constant in the section 31f, and decreases linearly in the section 13g until the linear motor rotor 10 is at the bottom dead center X_UTPAnd stops. Characteristic curve 32 shows the acceleration of linear motor rotor 10 as a function of time t, linear motor rotor 10 being accelerated at a constant positive acceleration in sections 32a and 32g, decelerated at a constant negative acceleration in sections 32c, 32e, and not moved at an acceleration in sections 32b, 32d, and 32 f. Characteristic curve 33 shows the force of the linear motor 14 applied to the linear motor rotor 10 as a function of time t, wherein a constant acceleration force is applied in section 33a, a small constant force is applied in section 33b to overcome the frictional force applied during the movement of the linear motor rotor 10, and a counter force is applied in section 33c to force the linear motor rotor 10 at the top dead center X_OTPAnd stops. During the stop, i.e. during the section 33d, no acceleration is applied. Thereafter, the linear motor rotor 10 is accelerated again in section 33e with constant force, kept in motion against the applied friction force by a small constant force acting in section 33f, and braked to stop at bottom dead center X by a constant force acting in section 33g_UTP. During the sections 33c and 33g, the linear electric machine 14 brakes the linear electric machine rotor 10, in the course of which the released energy can be converted into heat, wherein during the sections 33c and 33g the linear electric machine 14 preferably operates as a generator, while the electrical energy released in the course of this is temporarily stored in an energy store, preferably a control device.

The linear motor 14 can be controlled by means of a multiplicity of possible corresponding controls which are dependent on the time t or the travel X, wherein preferably at least one of the characteristic curves of travel, speed, acceleration and motor force is predetermined as being dependent on t, wherein the control device controls the linear motor 14 such that it moves at least approximately according to the predetermined characteristic curve. Fig. 6 shows another example of the control of the linear motor 14. Characteristic curve 34 shows the travel X of linear motor 14 in relation to time t during a complete cycle. Characteristic 35 shows the speed of the linear motor 14 as a function of time t, characteristic 36 shows the acceleration of the linear motor 14 as a function of t, and characteristic 37 shows the motor force of the linear motor 14 as a function of time t. Until time t1, the characteristic according to fig. 6 shows a similar process to the characteristic according to fig. 5, wherein the time axis in fig. 6 is significantly shorter, i.e. the movement in fig. 6 is significantly faster, compared to fig. 5, which can also be seen from the fact that the values of speed, acceleration and motor force in fig. 6 are much higher.

A further control example of the linear motor 14 is shown by the characteristic curve shown in fig. 6 between time T1 and the total cycle time T (i.e. the completion of the entire cycle). The control method has the following advantages: all the characteristic curves 34, 35, 36 and 37 vary continuously between time t2 and time t3 and without an inflection point, which means that the operation of the linear motor 14 is more gradual, since an inflection point usually causes a sudden change in the operating behavior, resulting in an increase in the mechanical load. The control example shown in fig. 6 is only one example of many possibilities for controlling the linear motor 14. The feasibility of operating the linear motor 14 with a plurality of different characteristic curves as a function of time yields the advantage that the reciprocating piston compressor 15 driven by such a linear motor 14 can be operated in a plurality of ways. Preferably, the linear motor 14 is operated such that the linearly movable free-piston device 16 is assigned at least one state variable Z which is dependent on the time t or on the stroke X_sollThe linear motor 14 is controlled in an adjustable manner, which results in the free-piston device 16 having or at least approximately having a given state variable Z_soll. Such a control method allows, for example, the operation of the linear motor compressor 1 to be optimized with respect to key indicators that can be predefined, since, for example, the maximum force output by the linear motor 14, the maximum power required for operating the linear compressor 1, the maximum acceleration occurring and/or the maximum speed occurring are predefined and must not be exceeded during operation.

As shown in fig. 1 and 2, the linear motor compressor 1 includes a linear motor 14 and a reciprocating piston compressor 15 driven by the linear motor 14. The overall kinematics of the motion of the linear motor compressor 1 is therefore substantially determined by the kinematics of the linear motor 14 in combination with the kinematics of the reciprocating piston compressor 15, the reciprocating piston compressor 15 being connected to the linear motor 14, the overall kinematics being substantially determined by: the inertial forces acting, the electromagnetic forces caused by the linear motor 14, the gas forces caused by or acting in the reciprocating piston compressor 15, the gas forces acting in the reciprocating piston compressor 15, and the friction forces caused by the movement of the piston and the linear motor 14.

The kinematics of the motion of the free-piston device 16 are described in more detail below by establishing equations of motion.

As shown in fig. 2, the two pistons 3, 4 are driven to reciprocate in the stroke direction X by the force generated by the linear motor 14. The first piston 3 being at bottom dead center X_UTPAnd top dead center X_OTPIn the positive stroke direction X. The first piston 3 being at bottom dead center X_UTPAnd top dead center X_OTPIn the positive stroke direction X. The second piston 4 moves in the direction opposite to the first piston 3, and as shown in fig. 2, in the forward stroke direction X, at the top dead center X_oTPAnd bottom dead center X_UTPMove within the range therebetween. Since the two pistons 3, 4 are moved in opposite directions, the analysis of the movement of the free piston device 16 takes into account only the first piston 3 in the positive X direction from the bottom dead center X_UTPMove to the upper dead point X_OTPAnd returns to the bottom dead center X_UTPThe cycle of (2). According to the simplified model, the equation of the driving force FLM applied by the linear motor 14 to move the free piston device 16 is as follows:

where mg is the total mass of the free piston device 16, x is the displacement and stroke of the free piston device, Fpr and Fp1 are the forces acting on the first and second pistons 3, 4 due to the respective gas pressures in the right second and left first compression chambers 5b, 5a, and Ffr and Ffl are the frictional forces of the right second piston 4 and left first piston 3, respectively.

The forces exerted by the gas pressure on the first and second pistons 3, 4, respectively, can be calculated according to the following formula:

wherein d is_pThe diameters of the first and second pistons 3, 4, respectively, P_iThe air pressures in the second right-side compression chamber 5b (i ═ 1) and the first left-side compression chamber 5a (i ═ r), respectively.

In view of the known overall kinematics of the linear motor compressor 1, the state variable Z can be specified for the control device_sollWhereby the control device controls the linear motor 14 such that the linear compressor 1 has at least approximately a defined state variable Z_soll。

In the simplest case, the travel displacement point X₁(i.e., the point defined along the stroke X), and the set velocity V of the free-piston device 16_sollAnd/or setting the acceleration a_nomalAnd/or setting the force F_sollCan be specified as a state variable Z_soll. Instead of the travel displacement point X₁It is also possible to specify the travel displacement time T_L1I.e. the time defined within the total cycle time T, preferably using bottom dead center X_UTPAs a time measurement reference. Thus, in the simplest case, the stroke time T of the free piston device 16_L1And a set speed v assigned thereto_sollAnd/or setting the acceleration a_nomalAnd/or setting the force F_sollCan also be specified as a state variable Z_soll. For example, as shown in fig. 9, if there is a problem in ensuring that the speed of the free-piston device 16 decreases in the region of points B and D, the state variable Z is_sollIt suffices that it specifies the stroke displacement point X₁Velocity v of_sollAnd stroke displacement X₂Velocity-v of_soll. In a similar manner, it is of course also possible to displace over the strokePoint specified target acceleration a_sollAnd/or target force F_soll。

Advantageously, along at least a partial section of the stroke displacement X and preferably along the entire stroke displacement X_LHeld state variable Z_sollIs assigned as the state variable Z_soll。

In a further advantageous method, the state variable Z is held during a part of the total cycle time T and preferably during the total cycle time T_sollIs assigned as the state variable Z_soll。

In a further advantageous method, the bottom dead center X_UTPAnd top dead center X_OTPAnd/or top dead centre X_OTPAnd bottom dead center X_UTPThe velocity-displacement curve in between is specified as the state variable Z_sollThe free piston device 16 moves back and forth according to this curve during operation of the linear motor compressor 1 shown in fig. 2. Figure 7 shows an example of such a method of operation of a linear motor compressor 1 comprising both a linear motor 14 and a reciprocating piston compressor 15. FIG. 7 shows the state variable Z as a function of the operating method according to the invention_sollVelocity-displacement curve G₁、G₂、G₃、G₄The method of operation is explained with the aid of fig. 2. The diagram according to fig. 7 shows on the left the movement of the first piston 3 starting from point a to the left of point a, bottom dead center X_UTPAccording to curve G₁Moving to point C through point B shown in FIG. 1, top dead center X_OTPMoves back to point A, i.e. bottom dead center X, via point D according to curve G2_UTP. The diagram according to fig. 7 is shown on the right of point a as state variable Z_sollOf the second piston 4-a velocity-displacement curve G₃、G₄. Since the second piston 4 moves in the opposite direction to the first piston 3, the second piston 4 moves in the opposite direction to the first piston 3 because of the curve G₃From point C, i.e. top dead centre X, the second piston 4_OTPMoves to a point A, i.e., a bottom dead center, via a point D shown in FIG. 1, and follows a curve G₄The second piston 4 moves back to point C, the top dead center X, via point B_OTP. Since the first and second pistons 3, 4 are fixed to each other and therefore have the same speed, except for the speedOutside the sign of the degrees, curve G₁And G₃In other respects have the same orientation. For the same reason, curve G₂And G₄Also exhibit the same trend but with a different sign of the speed. Preferably, the linear motor compressor 1 is at the bottom dead center X_UTPAnd top dead center X_OTPBetween and at top dead center X_OTPAnd bottom dead center X_UTPWith the same state variable Z on the return path in between_sollOr the same speed-displacement curve, except for the sign of the speed, so that all curves have the same curve G₁、G₂、G₃、G₄. As shown in fig. 7, the first piston 3 has a first average speed V between points a and B of the compression phase AB_m1The piston 3 has a second mean speed V between the points B and C of the discharge phase BC_m2First average velocity V_m1Greater than the second average speed V_m2. The average speed is understood to be the average of the speed of the piston 3 or 4 between two points. Thus, the first average speed V_m1Corresponding to the average speed between points A and B, a first average speed V_mlThe time integral corresponding to the velocity v (t) between points a and B is divided by the time required for the piston 3 to move between points a and B, respectively. First average speed V_m1The integral of the velocity v (X) corresponding to the displacement X between points a and B is divided by the path distance a-B required to move the piston 3 between points a and B. Similarly, the second average speed V_m2Thus corresponding to the average speed between points B and C, respectively, the second average speed V_m2The integral corresponding to the velocity v (t) or v (x) between points B and C is divided by the time or path distance B-C, respectively, required for the piston 3 to move between points B and C.

As shown in fig. 7, during the return movement from point C to point a, the first piston 3 has a third average speed V between points C and D of the expansion phase CD_m3And between points D and A of the intake phase DA the piston 3 has a fourth average speed V_m4Third average velocity V_m3Greater than fourth average speed V_m4. Therefore, the third average speed V_m3Corresponding to the average speed between points C and D, respectively, the third averageVelocity V_m3The integral corresponding to the velocity v (t) or v (x) between points C and D, respectively, is divided by the time or distance C-D required for the piston 3 to move between points C and D, respectively. Similarly, the fourth average speed V_m4And therefore corresponds to the average speed between points D and a, or the fourth average speed V_m4The integral corresponding to the velocity v (t) or v (x) between points D and a is divided by the time or distance D-a required for the piston 3 to move between points D and a, respectively.

The linear motor compressor 1 is preferably operated such that the pistons 3 and 4 have the same speed-displacement curve G in their reciprocating movement, except for the mirror image required on the shaft according to fig. 7₁And G₄Or the same speed-displacement curve G₂And G₃. In another possible operating mode, it is also possible for the two pistons 3 and 4 to each have a different speed-displacement curve in their reciprocating movement, for example their movement from right to left has a different speed-displacement curve than their movement from left to right.

The interaction of the linear motor 14 and the reciprocating piston compressor 15 can also be derived, for example, from the speed-displacement curve G shown in fig. 7₁As will be appreciated. Starting from point A to a travel point X₃Curve G₁A relatively fast increase is shown, in particular due to the fact that a small force is still required in the reciprocating piston compressor 15 at the beginning of the compression phase. In addition, the second compression chamber 5b or the gas therein is in an expansion phase, so that the gas drives the second piston 4, so that the combination of the driving force of the linear motor 14 and the expansion force acting on the second piston 4 results in a fast movement, i.e. an increased speed V or acceleration of the free piston device 16. In a further advantageous method, the free-piston device 16 is driven by the linear motor 14 so quickly that the expansion force contributes negligibly or not at all to the movement of the free-piston device 16. At the point of travel X₃In the subsequent stroke direction X, the compression power absorbed by the reciprocating piston compressor 15 steadily increases, so that the speed of the free piston device 16 decreases, in particular if the linear motor 14 is operated at constant power. After point B, the discharge valve 6a opens and the speed of the free piston device 16 is reduced byThe flow resistance occurring at the discharge valve 6a is further reduced. From the point of travel X₄To start, the free-piston device 16 must be braked and stopped until the top dead center X_OTPThis is preferably done by a linear electric motor 14 generating braking force and advantageously operating as a generator, the generated electric energy being preferably temporarily stored in the control device, for example in order to be in the section a-X₃Again accelerating the free-piston device 16.

FIG. 7 shows the state variable Z_sollVelocity-displacement diagram (v-x diagram). Instead of a speed-distance diagram, one of the characteristic curves 30 to 37 shown in fig. 5 or 6, for example the travel, the speed, the acceleration or the force as a function of time, can also be assigned to the state variable Z_soll. Furthermore, it is also possible, for example, to select the state variable Z_sollA combination of several of the characteristic curves 30 to 37 shown in fig. 5 or 6 is specified such that, for example, the maximum speed and/or acceleration and/or the force to be output by the linear motor 14 and/or the electrical energy consumed by the linear motor 14 is not exceeded.

In an advantageous method, the free-piston device 16 is set to a predetermined speed-displacement curve G during the compression phase AB₁From bottom dead centre X_UTPTo the opening point B of the discharge valve 6 so that the linear motor 14 has to output a constant or substantially constant power. Power applied by the linear motor 14_LMMultiplied by the velocity V of the free piston device 16. With a predetermined constant power, a predetermined velocity-displacement curve G1 can therefore be calculated. The advantage of this method is that the linear motor compressor can also be operated safely at lower power.

During continuous operation of the linear motor compressor 1, it has an expansion phase CD between points C and D, during which the gas located in the dead volume Vtot expands. In one possible method, the linear motor 14 can be operated as a generator at least along a partial section of the expansion phase CD, since the linear motor 14 brakes the movement of the pistons 3, 4 caused by the expansion force by means of the generator operation, the electrical energy generated in the process preferably being temporarily stored. In a particularly advantageous method, the linear motor 14 is along at least a portion of the expansion phase CD and preferablyIs controlled during the entire expansion phase CD such that the linear motor 14 does not exert an active braking action on the free-piston device 16 during the entire expansion phase CD, preferably such that the linear motor 14 exerts a positive braking action on the free-piston device 16 during the entire expansion phase CD, and preferably at points C and a, i.e. during the entire phase CA, towards the bottom dead center X_UTPExerts a positive force on the free piston device 16 acting in the direction of (a). This method ensures that the energy released by the gas located in the dead space Vtot during expansion along the expansion phase CD is preferably completely converted into kinetic energy of the free piston device 16, which facilitates the compression of the gas located in the second compression chamber 5b by the second piston 4 transferring the kinetic energy of the free piston device 16 to the gas.

Fig. 8 shows a further advantageous method of operation of the linear motor compressor 1 shown in fig. 2. Fig. 8 shows a rather schematic, i.e. slightly idealized, speed-distance diagram of the first piston 3, wherein the diagram shows the speed of the first piston 3 in relation to the stroke X during phase AC for simplifying the process that takes place, and the diagram subsequently shows the speed of the first piston 3 in relation to the stroke X during phase CA on the right side, in contrast to fig. 7, for better illustration, the stroke X during the CA phase being shown as travelling to the right. The first piston 3 itself is at the bottom dead center X at both the beginning and the end of the diagram shown in fig. 8_UTP. Predetermined state variable Z_sollIs curve G of the free piston device 16₁And G₂I.e. the velocity-displacement curve as shown in fig. 8. The compression phase AB is operated at a relatively high speed, in particular at a relatively high first average speed V_m1Lower, and therefore relatively fast in time. In the region of the opening point B of the outlet valve 6, the speed V decreases, so that the free-piston device 16 moves at a reduced speed during the discharge phase BC or at a lower second average speed V compared to the compression phase AB_m2And (4) moving. From bottom dead centre X_UTPInitially, the free-piston device 16 moves during the compression phase AB up to the opening point B of the discharge valve 6 and subsequently during the discharge phase BC to the closing point C of the discharge valve 6, so that a predetermined state variable Z_sollPredetermined speed-displacement curve or predetermined speed-timeMiddle curve, so that the first average speed V during the compression phase AB_m1Above a second average speed V during the discharge phase BC_m2And/or the duration of the compression phase AB is shorter than the duration of the discharge phase BC. In particular, this method has the advantage that the duration of the expulsion phase BC can be increased. The advantage of this method is that the free piston device 16 can be run at a reduced speed during the discharge phase BC, i.e. during the outflow of gas from the outlet valve 6a, which reduces the outflow resistance caused by the outlet valve 6a and thus also reduces the energy loss caused by the outflow. Since no bleeding occurs during the compression phase AB, the compression phase AB may be run at an increased speed or at a higher average speed with no or very low additional energy, so that the discharge phase BC may preferably be prolonged in time by running through the discharge phase BC at a lower average speed than the compression phase AB. This has the advantage that the energy losses caused by the gas flowing out of the outlet valve can be reduced. For a given cycle time Tz of the complete reciprocating movement of the linear motor compressor, the linear motor compressor is advantageously operated such that the first mean speed V is set during the compression phase AB_m1Is set high, preferably as high as possible, and a second average speed V_m2Is set to be lower than the first average speed V_m1Preferably as low as possible, but such that a given cycle time Tz of the full reciprocating movement is maintained. Thus, at a given cycle time Tz, the method can extend the duration of the discharge phase BC or reduce the flow rate of the gas flowing out of the interior of the cylinder at the discharge valve 6a, which reduces the energy consumption occurring at the discharge valve. This process can improve the efficiency of the linear motor compressor. In a particularly advantageous method, the linear motor 8 drives the free piston device 16 by means of the electric motor at least during a partial section of the compression phase AB, wherein the linear motor 8 brakes the free piston device 16 at least during a partial section of the discharge phase and is preferably operated here as a generator which releases electrical energy which is preferably temporarily stored and preferably reused during the compression phase AB to supply the linear motor 8 with electrical energy. This short-term intermediate storage of electrical energy allows linear motor compressionThe machine operates particularly efficiently, in particular ensuring a first average speed V during the compression phase AB_m1Above a second average speed V during the discharge phase BC_m2. According to curve G₂State variable Z of_sollThe movement of the free piston device 16 during a phase CA is shown, respectively the first piston 3 from the top dead center X_OTPTo the bottom dead center X_UTPThe movement of (2). If the linear motor compressor 1 has the first and second compression chambers 5a, 5b, which are compressed by the pistons 3, 4 rotating in opposite directions as shown in fig. 2, the two curves G, except for the sign of the velocity v, are shown in fig. 8₁、G₂Having the same orientation. If the linear motor compressor 1 has only one first compression chamber 5a, the two curves G₁And G₂It is also possible to have different curves. Mean velocity V of CD during the expansion phase_m3Average speed V higher than suction phase DA_m4As shown in fig. 8.

Fig. 9 shows another operation method of the linear motor compressor 1 shown in fig. 2. Fig. 9 shows a velocity-displacement diagram of the first piston 3. As predetermined state variable Z_sollCurves G1 and G2 are assigned to the free piston device 16. These curves G1 and G2 are chosen such that the first and second pistons 3, 4 move in the region of points A, B, C and D at a low or reduced speed v, respectively, the speed at points C and a decreasing to 0m/s, since the free piston device will momentarily stop at these reversal points. Preferably, the speed in the region of points C and a, i.e. in particular immediately before points C and a are reached, is reduced to a particularly great extent such that the speed is lower than the speed of points B and D. Fig. 9a and 9b show in detail the velocity of fig. 9 in the region of points C and a, respectively. In an advantageous process, the velocities at points C and A are very low and are, for example, less than 0.1 m/s. The reduced speed at points C and a has the effect of causing the inlet valve 7a and the outlet valve 6a, respectively, to close at a slow speed, which has the effect that these valves are subjected to only slight mechanical stress by this gentle closing, so that the valves can be operated reliably, preferably for a long period of time, without maintenance. As shown in fig. 9b, the free piston device 16 is first directed towards the end of the stroke, towards the bottom dead centre X_UTPDecelerating with a greater negative acceleration and then decelerating with a reduced negative acceleration, whereby the free-piston device16 at bottom dead center X with reduced negative acceleration_UTPDecelerates until it stops and then accelerates again in the opposite direction. As shown in fig. 9a, the free piston device 16 is first directed towards the end of the stroke, towards the top dead centre X_OTPDecelerating with a greater negative acceleration and then decelerating with a reduced negative acceleration, whereby the free-piston device 16 decelerates with a reduced negative acceleration to the top dead center X_OTPStops and then accelerates again in the opposite direction. In the simplest case, the state variable Z_sollMay consist of only a single point, as shown in FIG. 9, e.g. having the value v_sollTravel displacement point X of₁. Control is thus effected such that the free piston device 16 moves at the stroke displacement point X₁Has a velocity v_soll. This ensures that the free piston device 16 is at the stroke displacement point X₁At a velocity having a desired low velocity v_soll。

Fig. 10 shows a drive device 20 for operating the linear motor compressor 1. The control device 27 detects at least one actual state variable 29a of the linear motor compressor 1, preferably the stroke X and/or the velocity v and/or the acceleration and/or the applied force F of the free piston device 16, by means of at least one sensor 21 via a signal line. State variable Z_setThe set value of (a) is preset by a set value presetting device. The control device 27 controls the actual state variable 29a and the set state variable Z_setpoint29e calculate a control signal 29b which is fed to the inverter control 26. The inverter control device 26 drives the power supply 23 and the inverter 22 via control lines 29c, 29d, wherein the inverter 22 comprises a plurality of drives for individually driving a plurality of stator windings 12a, 12b, 12c, 12d via electrical conductors 24a, 24b, 24c, 24 d. The power supply 23 is connected to the inverter 22 through a power line 25. In a particularly advantageous embodiment, the power supply 23 comprises an energy storage device, wherein the inverter 22 is controllable such that electrical energy can be extracted from the linear motor compressor 1 and supplied to the power supply 23 via the inverter 22, the electrical energy being stored in the power supply for a preferably short time, preferably within a time period of less than one second or less than one minute.