SYSTEM COMPRISING A REFRIGERANT COMPRESSOR AND METHOD FOR OPERATING THE REFRIGERANT COMPRESSOR

Abstract

A system includes a refrigerant compressor and an electronic control device therefor. The compressor includes a drive unit and a compression mechanism drivable thereby having a crankshaft-drivable piston. The control device captures and controls, in an open- and/or closed-loop manner, the crankshaft rotational speed and at least approximately captures the piston position. The control device determines an energy evaluation variable difference while the drive unit is switched off proportional to the energy required to perform one crankshaft revolution; at a measurement rotational speed, determines an energy evaluation variable proportional to the rotational energy at the measurement rotational speed; determines the number of crankshaft revolutions remaining, while the drive unit is switched off, until a standstill of the compression mechanism; and checks whether the remaining crankshaft revolutions upon switch-off of the drive unit at a reference piston position enable stopping of the compression mechanism in the suction phase thereof.

Description

FIELD OF THE INVENTION

The present invention relates to a system comprising a refrigerant compressor and an electronic control device for the refrigerant compressor, which refrigerant compressor at least comprises

a drive unit,

a compression mechanism standing in an active connection with a rotor of the drive unit, having at least one piston that can. move back and forth in a cylinder of a cylinder block and can be driven by way of a crankshaft, so as to draw refrigerant into the cylinder during a suction phase and to compress the refrigerant in the cylinder during a compression phase that follows the suction phase,

wherein the electronic control device is set up for

capturing a rotational speed of the crankshaft and controlling and/or regulating it,

at least approximately capturing a piston position of the piston.

The present invention furthermore relates to a method for operation of a refrigerant compressor having a drive unit, a compression mechanism that can be driven by means of the drive unit, comprising a piston as well as a crankshaft that stands in connection with the piston by way of a connecting rod.

STATE OF THE ART

Such electronic control devices are used in the case of refrigerant compressors that are regulated on the basis of a variable rotational velocity, i.e. a variable rotational speed, in particular also in the case of refrigerant compressors that are based on the reciprocating principle. Refrigerant compressors based on a variable rotational speed have the advantage that they can be more specifically coordinated with refrigeration demands of the object to be cooled, for example in that they can be operated at a lower rotational speed in the case of lower refrigeration demands, and at a correspondingly increased rotational speed in the case of an increased refrigeration demand.

The structure of piston refrigerant compressors based on a variable rotational speed is sufficiently known. They essentially consist of a drive unit and a compression mechanism in the form of a piston that moves back and forth between a top and a bottom dead center in a cylinder housing, which piston is connected with a crankshaft by way of a connecting rod, which in turn is coupled, in torsionally rigid manner, with a rotor of the drive unit.

Typically, a brushless direct-current motor is used as a drive unit. In this regard, it is possible to determine the relative position of the rotor of the direct-current motor and thereby also the rotational velocity as well as the rotational speed of the motor or of the compression mechanism on the basis of the counter-voltage induced in the motor coil (induction counter-voltage). This method makes do without separate sensors and is therefore particularly easy to implement and demonstrates low susceptibility to problems.

The stopping process is problematic in the case of piston refrigerant compressors. In the operating state of the refrigerant compressor, different gas forces act on the compression mechanism in the suction phase and the compression phase (due to the refrigerant pressure ratios in the system), as do friction forces (both together are referred to as the load torque); looking at the situation more precise this results in a rotational velocity that is non-uniform over the crank angle, because it varies. In the present application, a distinction is fundamentally made between the terms rotational speed and rotational velocity. The term rotational velocity is used when the actual, current rotational velocity is meant, which varies over the crank angle in the case of piston refrigerant compressors according to the state of the art, whereas the term rotational speed is used when the average rotational speed of a crankshaft revolution is meant, in other words that value which is generally meant when speaking of the rotational speed of a piston refrigerant compressor.

In concrete terms, during the compression phase, which essentially corresponds to a movement of the piston from the bottom dead center to the top dead center, a load torque that is increased in comparison with the suction phase acts on the compression mechanism and must be overcome by the operating torque of the drive unit, so as to keep the compression process going. In the case of piston refrigerant compressors according to the state of the art, which are operated at a constant voltage, the increased load torque in the compression phase leads to a reduction in the rotational velocity of the compression mechanism in the compression phase.

During the suction phase, which essentially corresponds to a movement of the piston from the top to the bottom dead center, in contrast, the gas forces bring about a reduced load torque as compared with the compression phase. This leads to an increase in the rotational velocity of the compression mechanism during the suction phase.

In total, therefore, a load torque that varies over the crank angle acts on the compression mechanism, wherein the range of variation of the load torque depends, above all, on the pressure ratio in the refrigerant circuit and leads to differently great angle accelerations of the compression mechanism during a crankshaft revolution and thereby to a non-uniform rotational velocity over the crank angle.

In order to balance out oscillations and vibrations of the compression mechanism during operation, this mechanism, including the drive unit, is mounted in a housing by way of spring elements. However, the inherent frequencies of this oscillation system lie between 5 Hz and 16 Hz, depending on the compressor type.

Thereby the increased load torque that recurs during every crankshaft revolution during the compression phase leads to impacts on the compression mechanism, in particular during operation of the piston refrigerant compressor at rotational velocities or rotational speeds below a range between 1000 rpm and 700 rpm, which impacts press the compression mechanism including drive unit into the spring elements and deflect these, wherein the impact frequency lies in the range of the inherent frequency of the oscillation system, so that the deflections of the spring elements increase with every crankshaft revolution, in such a manner that the compression mechanism and; or the drive unit can hit against the housing, and as a result, undesirable noise emissions can occur. This circumstance is also a reason why known piston refrigerant compressors are not operated below a range between 1000 rpm and 700 rpm in the normal, regulated operating phase.

However, the undesirable noise emissions of a piston refrigerant compressor, as described, at low rotational velocities/rotational speeds, occur not only in normal, regulated operation but also, above all, during the stopping process, where these low rotational velocities/rotational speeds must be traversed. The stopping process generally proceeds as follows:

When the target temperature of the object to be cooled, for example of a refrigeration compartment of a refrigerator, has been reached after a correspondingly lasting, normal, regulated operating phase of the refrigerant compressor, the electronic control device of the refrigerator sends a signal to the electronic control device of the refrigerant compressor, with which this device is informed that no cooling output is required any longer, since the target temperature has been reached. From the state of the art, it is known that thereupon the electronic control device of the refrigerant compressor shuts off the drive (shut-off point in time) and the stopping process begins.

The crankshaft of the compression mechanism passes through complete revolutions, in each instance, even after the shut-off point in time, starting at the top dead center (crank angle 0°), wherein at first, a suction phase (correctly: suction and re-expansion phase) occurs, during which refrigerant is drawn into the cylinder. This suction phase ends, theoretically, when the cylinder has reached the bottom dead center (crank angle 180°). After that, the compression phase (correctly: compression and push-out phase) begins, during which the refrigerant situated in the cylinder is compressed and pushed out of the cylinder. The compression phase ends, theoretically, when the piston has reached the top dead center (crank angle 360°) once again. In practice, however, the actual compression of the refrigerant begins only at a crank angle of approximately 210° (depending on the refrigerant compressor, the pressure ratios, the valve design, etc.), but in any case after 180°, and the suction phase begins at approximately 30°, but in any case after the top dead center.

Shut-off of the drive unit of the refrigerant compressor at a shut-off point in time initiates the stopping process and leads to the result that the compression mechanism is in a drive-free state (without operating torque) and only continues to rotate on the basis of its mass inertia, until it has come to a complete standstill, i.e. its rotational velocity or rotational speed is 0. Speaking colloquially, one could also say that the refrigerant compressor “is running down.”

During the drive-free state, the compression mechanism and the drive unit move exclusively on the basis of the kinetic energy that they have at the shut-off point in time, as well as the mass inertia. They therefore rotate in uncontrolled manner, so to speak, and their rotational velocity behavior or rotational speed behavior is dependent on the load torque acting on the compression mechanism. The load torque leads to a reduction of the rotational velocity or the rotational speed of the refrigerant compressor, which is running down in drive-free manner, so that the kinetic energy of the compression mechanism becomes less and less until it possibly no longer suffices to overcome the load torque, as a function of the pressure ratios in the refrigerant circuit.

In this regard, the case in which the piston is just in a compression phase when the kinetic energy of the compression mechanism/of the drive unit is no longer sufficient to overcome the load torque, and the piston of the compression mechanism is being pressed back in the direction of the bottom dead center, wherein the rotational direction of the compression mechanism is thereby reversed, is particularly problematic. In other words, the kinetic energy is no longer sufficient to end the compression phase and push out the compressed refrigerant, so that the compressed refrigerant expands in the cylinder again and thereby presses the piston back in the direction of the bottom dead center.

An additional stopping jolt that acts on the compression. mechanism is connected with the reversal of the rotational direction, which jolt presses the compression mechanism/the drive unit into the spring elements and additionally deflects them.

Specifically during the stopping process, where no positive operating torque counteracts the load torque, as has already been described above, the stopping jolt contributes decisively to the deflection of the spring element, due to the reversal of the rotational direction, so that the likelihood that the compression mechanism/the drive unit makes contact with the housing wall and thereby undesirable noise emissions are caused is significantly increased. This effect essentially results from the principle of conservation of momentum, according to which the stopping jolt is balanced out by a counter-deflection of the drive unit. In particular for drive units having reduced mass inertia torques, such as brushless direct-current motors (Brushless DC Motors), for example, the same stopping jolt leads to a correspondingly greater deflection.

From the state of the art, it is known to end the drive-free phase by application of a braking torque and to thereby prevent at least a kick-back of the refrigerant compressor and thereby of the stopping jolt. In concrete terms, it is known from EP 2669519 A1 and the document DE202012013046 U1 that is branched off from it to brake the compression mechanism/drive unit that is rotating in drive-free manner after the shut-off point in time, when the rotational speed drops below a specific value, by means of a braking torque. For this purpose, it is necessary to constantly monitor the rotational speed of the compression mechanism that is rotating in drive-free manner after the shut-off point in time, and at a defined rotational speed, which still has to be sufficiently high to overcome the load torque up to that point, to actively brake the compression mechanism by means of a braking torque that is applied to the compression mechanism.

A disadvantage of the state of the art expresses itself in that the active braking process negatively influences the energy efficiency of the refrigerant compressor, since braking energy must be applied during every stopping process. In addition to this, the braking torque will already be applied at a relatively high rotational speed; this is disadvantageous in terms of energy, and furthermore also causes additional noise emissions.

TASK OF THE INVENTION

It is therefore the goal of the invention to provide a system having a refrigerant compressor, preferably a piston refrigerant compressor, and an electronic control device for the refrigerant compressor, as well as a method for operation of a refrigerant compressor, preferably of a piston refrigerant compressor, which reliably prevent the occurrence of the stopping jolt, without a braking torque having to be actively applied for this purpose, thereby making optimized operation of the refrigerant compressor possible with regard to energy efficiency and noise emissions.

PRESENTATION OF THE INVENTION

The core of the present invention for accomplishing the task stated above is not to leave significant parameters of the stopping process up to chance, but rather to set them in such a manner that if possible, no stopping jolt occurs after the drive unit is shut off, while the compression mechanism runs down, in that the compression mechanism comes to a standstill in the suction phase. In this way, the possibility is excluded that a further compression phase is started and therefore a stopping jolt occurs. In concrete terms, it is provided, according to the invention, in the case of a system comprising a refrigerant compressor and an electronic control device for the refrigerant compressor, which refrigerant compressor at least comprises

a drive unit,

a compression mechanism that stands in an active connection with a rotor of the drive unit, having at least one piston that can move back and forth in a cylinder of a cylinder block, which piston can be driven by way of a crankshaft, so as to cyclically draw refrigerant into the cylinder during a suction phase and to compress the refrigerant in the cylinder during a compression phase that follows the suction phase,

wherein the electronic control device is set up for capturing a rotational speed of the crankshaft and for controlling and/or regulating it,

at least approximately capturing a piston position of the piston, that the electronic control device is set up for determining, when the drive unit is shut off, an energy evaluation variable difference that is proportional to the energy required to perform one crankshaft revolution, at a measurement rotational speed, determining an energy evaluation variable that is proportional to the rotational energy at the measurement rotational speed, along with the number of crankshaft revolutions remaining until standstill of the compression mechanism when the drive unit is shut off, checking whether the remaining crankshaft revolutions at shut-off of the drive unit allow stopping of the compression mechanism in its suction phase at a reference piston position, if necessary, turning the drive unit on and, taking into consideration the energy evaluation variable difference, determining a shut-off rotational speed at which the drive unit must be shut off at the reference piston position, so as to bring about a standstill of the compression mechanism in the suction phase and to shut off the drive unit at the shut-off rotational speed,

or, if necessary, turning the drive unit on and operating it at a limit rotational speed that can be predetermined, and, taking into consideration the energy evaluation variable difference, determining a shut-off piston position and shutting the drive unit off at the limit rotational speed and the shut-off piston position.

Analogously, it is provided according to the invention, in the case of a method for operation of a refrigerant compressor having a drive unit, a compression mechanism comprising a piston as well as a crankshaft that stands in connection with the piston by way of a connecting rod, which mechanism can be driven by means of the drive unit, that the method comprises the following steps:

when the drive unit is shut off, determining an energy evaluation variable difference, which is proportional to the energy required for performing a crankshaft revolution, at a measurement rotational speed, determining an energy evaluation variable, which is proportional to a rotational energy at the measurement rotational speed, and calculating the number of crankshaft revolutions remaining until standstill of the compression mechanism, when the drive unit is shut off, checking whether the remaining crankshaft revolutions at shut-off of the drive unit allow stopping of the compression mechanism in its suction phase at a reference piston position, if necessary, turning on the drive unit and, taking into consideration the energy evaluation variable difference, determining a shut-off rotational speed at which the drive unit must be shut off at the reference piston position so as to bring about a standstill of the compression mechanism in the suction phase, and shutting off the drive unit at the shut-off rotational speed,

or, if necessary, turning on the drive unit and operating it at a limit rotational speed that can be predetermined, and, taking into consideration the energy evaluation variable difference, determining a shut-off piston position and shutting off the drive unit at the limit rotational speed and at the shut-off piston position.

Capturing the rotational speed fundamentally does not preclude that the rotational velocity can also be captured.

Clearly, piston position is understood to mean a current piston position, which can be indicated, in particular, as a crankshaft rotational position in degrees, wherein, for example, the top or bottom dead center of the piston can be defined as 0°.

The term “drive unit is shut off” is understood to mean that the drive unit does not generate any positive (in other words accelerating) or negative (in other words braking) operating torque, and the compression mechanism continues to run or runs down in drive-free manner, i.e. on the basis of mass inertia or the inertia torques of the rotor and compression mechanism. The drive unit is therefore not supplied with power or operated in the shut-off state, in practice. Of course, this does not preclude that due to unavoidable friction in the drive unit, for example, the drive unit exerts a certain negative torque on the compression mechanism in the shut-off state.

Rotational energy is stored in the rotating compression mechanism and rotor. If the inertia moment of the rotor as compared with that of the compression mechanism can be ignored, one can also say that the rotational energy is essentially stored in the compression mechanism. The energy evaluation variable difference is a measure of how much of this rotational energy is used up per crankshaft revolution when running down. The rotational energy used up per crankshaft revolution could also be referred to as the rotational energy decrement. In particular, it is sufficient if the energy evaluation variable stands in a specific ratio to the rotational energy decrement, which ratio is not necessarily known. Of course, the case is also conceivable where the ratio is simply 1:1, i.e. where a proportionality factor between the rotational energy decrement and the energy evaluation variable difference is simply 1. Since running down proceeds rapidly (typically within 1 to 2 seconds), the stress or the load torque caused by pressures and temperature practically does not change during running down. Consequently, it can be assumed, in a first approximation, that the energy evaluation variable difference in fact remains constant during the entire period of running down, in other words until a standstill of the compression mechanism or rotor occurs (the latter necessarily stands still when the compression mechanism stands still, and vice versa).

The energy evaluation variable at a specific measurement rotational speed, fundamentally any desired measurement rotational speed, is a measure of how great the rotational energy is at this measurement rotational speed. In particular, it is sufficient if the energy evaluation variable stands in a specific ratio to the rotational energy, which ratio is not necessarily known. Analogous to what has been said above, of course, the case is also conceivable where the ratio is simply 1:1, i.e. where a proportionality factor between the rotational energy and the energy evaluation variable is simply 1.

Correspondingly, the number of revolutions or the number of crankshaft revolutions remaining until standstill of the compression mechanism occurs can also be calculated, for the case that the drive unit is shut off at the measurement rotational speed being considered, by a simple division of the corresponding energy evaluation variable by the energy evaluation variable difference. By means of this quotient formation, the proportionality factor—which is possibly unknown—is eliminated for the rotational energy (in the case of the measurement rotational speed) and for the rotation decrement.

The term “stopping of the compression mechanism in its suction phase” is clearly understood to mean bringing the compression mechanism to a standstill in its suction phase.

On the basis of the information regarding the number of revolutions, the compression mechanism can be operated and allowed to run down by means of turning the drive unit on and off, in such a manner that the compression mechanism comes to a standstill. During shut-off, in this regard the piston position at which shut-off occurs must be appropriately taken into account with reference to the reference piston position.

The limit rotational speed, which can be predetermined, can be entered into a memory of the control device or can be stored there, if necessary. It can—but does not have—have the same value as the shut-off rotational speed.

In the case of a preferred embodiment of the system according to the invention, it is therefore provided that the control device is set up for

determining the energy evaluation variable difference by means of formation of the difference of the energy evaluation variables at two consecutive revolutions of the crankshaft, so as to be able to determine, by means of formation of the quotient of energy evaluation variable/energy evaluation variable difference, for how many revolutions the drive-free compression mechanism can continue to run, proceeding from the measurement rotational speed and the reference piston position, wherein it can be determined, on the basis of the post-decimal portion of the determined number of revolutions, whether the compression mechanism would come to a standstill in the suction phase or in the compression phase,

and, using the quotient format on and taking into account the post-decimal portion of the determined number of revolutions, to drive the compression mechanism in such a manner and to shut off the drive unit in such a manner that the compression mechanism comes to a standstill during the suction phase.

Analogously, it is provided, in the case of a preferred embodiment of the method according to the invention, that the energy evaluation variable difference is determined by means of formation of the difference of the energy evaluation variables at two consecutive revolutions of the crankshaft, is determined, by means of formation of the quotient of energy evaluation variable/energy evaluation variable difference, for how many revolutions the drive-free compression mechanism can continue to run, proceeding from the measurement rotational speed and the reference piston position, wherein it is determined, on the basis of the post-decimal portion of the determined number of revolutions, whether the compression mechanism would come to a standstill in the suction phase or in the compression phase,

using the quotient formation and taking the post-decimal portion of the determined number of revolutions into account, the compression mechanism is driven in such a manner and the drive unit is shut off in such a manner that the compression mechanism comes to a standstill during the suction phase.

The energy evaluation variable difference can be determined particularly easily and rapidly in the manner described when the drive unit is shut off and the compression mechanism is running down. Taking into consideration the post-decimal portion of the determined number of revolutions, it can be set in precise manner whether or not the compression mechanism comes to a standstill in the suction phase.

In the case of a preferred embodiment of the system according to the invention, it is provided that the control device is set up for shutting the drive unit off and determining the energy evaluation variable difference only when the rotational speed is greater than or equal to a minimum rotational speed, preferably one that can be predetermined. Analogously, it is provided, in the case of a preferred embodiment of the method according to the invention, that the drive unit is shut off and the energy evaluation variable difference is determined only when the rotational speed is greater than or equal to a minimum rotational speed, preferably one that can be predetermined. In particular, it can be ensured in this manner that after shut-off, two revolutions are still possible, so that the energy evaluation variable difference can be reliably and precisely determined. Once again, the minimum rotational speed can be entered into the memory of the control device or stored there.

In the case of a preferred embodiment of the system or method according to the invention, it is provided that the reference piston position is the top dead center (TDC) of the piston 1n the cylinder. The top dead center is weal-defined and is therefore very well suitable as a reference piston position.

In the case of a preferred embodiment of the system according to the invention, it is provided. that the electronic control device is set up for driving the compression mechanism in such a manner that the shut-off rotational speed (ω_shut-off) is reached, and for shutting the drive unit off at the shut-off rotational speed and the reference piston position, wherein. the shut-off rotational speed is determined in that the energy evaluation variable is determined at a determination rotational speed (ω_b) that functions as the measurement rotational speed, which is preferably present when the drive unit is shut off for determination of the energy evaluation variable difference, and the number of revolutions is calculated by means of quotient formation:

N=E(ω_b)/W,

an adapted number of revolutions (N′) is calculated, in that the number of revolutions is rounded up to the next greater whole number, and subsequently, an adaptation number between 0 and 1 is added, and

the shut-off rotational speed is calculated within a constant factor (c), as the root of the product of the adapted number of revolutions and. the energy evaluation variable difference:

ω_shut-off=C*(N′*W)^0.5.

Analogously, it is provided, in the case of a preferred embodiment of the method according to the invention, that the compression mechanism is driven in such a manner that the shut-off rotational speed (ω_shut-off) is reached, and the drive unit is shut off at the shut-off rotational speed and the reference piston. position, wherein the shut-off rotational speed is determined in that

the energy evaluation variable is determined at a determination rotational speed (ω_b) that functions as the measurement rotational speed, which is preferably present when the drive unit is shut off for determining the energy evaluation variable difference,

and the number of revolutions is calculated by means of quotient formation:

N=E(ω_b)/W,

an adapted number of revolutions (N′) is calculated, in that the number of revolutions is rounded up to the next greater whole number, and subsequently an adaptation number between 0 and 1 is added, and

the shut-off rotational speed is calculated within a constant factor (c) as the root of the product of the adapted number of revolutions and the energy evaluation variable difference:

ω_shut-off=C*(N′*W)^0.5.

By means of the addition of the adaptation number, it is ensured that the post-decimal portion of the adapted number of revolutions is such that with reference to the reference piston position, the compression mechanism reliably comes to a standstill in the suction phase. In other words, when. the compression mechanism comes to a standstill, the piston position must be sufficiently past the top dead center and sufficiently ahead of the compression phase, preferably ahead of the bottom dead center.

In the case of a particularly preferred embodiment of the system or method according to the invention, it is preferred that the determination rotational speed lies in a range of 500 min⁻ to 1500 min⁻¹, preferably of 800 min⁻¹ to 1200 min⁻¹. In this way, it is ensured that the determination rotational speed lies above a lowest operating rotational speed of the compressor, and the energy evaluation variable difference can be determined correspondingly reliably and precisely.

The constant factor c indicated above is accordingly guided by the way in which the energy evaluation. variable E(ω) is calculated. If E(ω)=ω² is simply used for the calculation of the energy evaluation variable, then c=1. Correspondingly, it is provided, in the case of a preferred embodiment of the system according to the invention, that the electronic control device is set up for determining the energy evaluation variable for the measurement rotational speed by means of squaring the measurement rotational speed. Analogously, it is provided, in the case of a preferred embodiment of the method according to the invention, that the electronic control device is set up for determining the energy evaluation variable for the measurement rotational speed by means of squaring the measurement rotational speed.

In the case of a preferred embodiment of the system according to the invention, it ls provided that the electronic control device is set up for driving the compression mechanism in such a manner that the limit rotational speed (ω_limit) is reached, and for shutting off the drive unit at the limit rotational speed and the shut-off piston position, wherein the shut-off piston position is determined in that

the energy evaluation variable at the limit rotational speed is determined,

the number of revolutions (N) is calculated by means of quotient formation:

N=E(ω_limit)/W,

the post-decimal portion of the number of revolutions is determined,

an adapted post-decimal portion is determined in that an adaptation number between 0 and 1 is subtracted from the post-decimal portion of the number of revolutions,

the adapted post-decimal portion is converted to a piston position, and the latter is deducted from the reference piston position.

Analogously, it is provided, in the case of a preferred embodiment of the method according to the invention, that the compression mechanism is driven in such a manner that the limit rotational speed (ω_limit) is reached, and the drive unit is shut off at the limit rotational speed and the shut-off piston position, wherein the shut-off piston position is determined in that the energy evaluation variable at the limit rotational speed is determined,

the number of revolutions (N) is calculated by means of quotient formation:

N=E(ω_limit)/W,

the post-decimal portion of the number of revolutions is determined, and an adapted post-decimal portion is determined in that an adaptation number between 0 and 1 is subtracted from the post-decimal portion. of the number of revolutions,

the adapted post-decimal portion is converted to a piston position, and this is deducted from the reference piston position.

In the case of this variant, the compression mechanism is therefore driven by means of the drive unit, in fixed manner, with the limit rotational speed that can be predetermined or has been predetermined. Instead of the shut-off rotational speed, a suitable piston position, namely the shut-off piston position, is determined, at which the drive unit is shut off so as to ensure that the compression mechanism comes to a standstill in the suction phase.

It should be noted that the minimum rotational speed must be greater than the limit rotational speed. In order to easily ensure this, it is provided, in the case of a particular embodiment of the system or method according to the invention, that the limit rotational speed lies in a range of 500 min⁻¹ 1500 min⁻¹, preferably of 800 min⁻¹ to 1200 min⁻¹.

In the case of a preferred embodiment of the system according to the invention, it is provided that the electronic control device is set up for

a) turning off the drive unit and

b) while the drive unit is shut off,

b1) determining the energy evaluation variable difference,

b2) determining the energy evaluation variable (E(ω_run-down)) for a run-down rotational speed (ω_run-down) that is then present and functions as the measurement rotational speed,

b3) calculating the number of revolutions (N) by means of quotient formation: N=E(ω_run-down)/W

b4) and comparing the post-decimal portion of the number of revolutions with an adaptation number between 0 and 1, and

c) if the post-decimal portion is greater than the adaptation number, driving the compression mechanism only for the duration of part of a complete revolution of the crankshaft.

Analogously, it is provided, in the case of a preferred embodiment of the method according to the invention, that

a) the drive unit is switched and

b) while the drive unit is shut off,

b1) the energy evaluation variable difference is determined,

b2) the energy evaluation variable (ω_run-down)) for a run-down rotational speed (ω_run-down) that is then present and functions as the measurement rotational speed is determined,

b3) the number of revolutions (N) is calculated by means of quotient formation: N=E(ω_run-down)/W

b4) and the post-decimal portion of the number of revolutions is compared with an adaptation number between 0 and 1, and

c) if the post-decimal portion is greater than the adaptation number, the compression mechanism is driven only for the duration of part of a complete revolution of the crankshaft.

In simplified terms, in the case of this variant it is first determined, during running down, whether the compression mechanism would come to a standstill in the suction phase (by means of comparison of the post-decimal portion of the number of revolutions determined for the run-down rotational speed that is currently present with the adaptation number). If the compression mechanism would not come to a standstill in the suction phase—or would not do so reliably enough—the compression mechanism is given a small “shove” so as to ensure its stopping in the suction phase. The said shove takes place in that the compression mechanism is driven only for a fraction of the duration of a complete crankshaft revolution, and this in turn is brought about by means of a correspondingly short turn-on of the drive unit.

It is conceivable that a one-time shove is not sufficient, to increase the rotational energy to such an extent and/or precisely enough so that the compression mechanism that is running down comes to a standstill in the suction phase. For this reason, it is provided, in the case of a particularly preferred embodiment of the system according to the invention, that the electronic control device (13) is set up for iteratively repeating at least the steps b2), b3), b4), and c). Analogously, it is provided, in the case of a particularly preferred. embodiment of the method according to the invention, that at least the steps b2), b3), b4), and c) are iteratively repeated.

In other words, the said steps are repeated until it is ensured that the compression mechanism, which is running down, will come to a standstill in the suction phase; this is determined in step c). In other words, it is decided in step c) whether or not a further iteration will be carried out.

Theoretically, it is also conceivable, in this regard, to repeat step b1), but in practice, this is usually not necessary, since the energy evaluation variable difference is at least approximately constant.

In the case of a particularly preferred embodiment of the system or method according to the invention, it is provided that the run-down rotational speed lies in a range of 500 min⁻¹ to 1500 min⁻¹, preferably of 800 min⁻¹ to 1200 min⁻¹. In the case of such a run-down rotational speed, the rotational energy can be increased in very precisely targeted manner by means of the shove. Correspondingly, it can be ensured in particularly reliable manner that the compression mechanism comes to a standstill in the suction phase.

As has already been stated, the top dead center is particularly well suited as the reference piston position. For this case, it is provided, in the case of a preferred. embodiment of the system or method according to the invention, that the (respective) adaptation number lies in the range of 0.1 to 0.4, preferably of 0.2 to 0.3, so as to guarantee that the compression mechanism comes to a standstill in the suction phase. This holds true for all three special cases described above, in which the determination rotational speed, the limit rotational speed or the run-down rotational speed is optionally used.

In the case of a particularly preferred embodiment of the system according to the invention, it is provided that the control device is set up for determining the energy evaluation variable difference in such a manner that multiple energy evaluation variable differences for rotational speeds are determined in the case of two consecutive revolutions, in each instance, in a sequence of more than two consecutive revolutions, and an average is formed from these energy evaluation variable differences. Analogously, it is provided, in the case of a particularly preferred embodiment of the method according to the invention, that the energy evaluation variable difference is determined in such a manner that multiple energy evaluation variable differences for rotational speeds are determined in the case of two consecutive revolutions, in each instance, in a sequence of more than two consecutive revolutions, and an average value is formed from these energy evaluation variable differences. By means of the said average value formation, the energy evaluation variable difference can be determined particularly precisely. Calculating the number of revolutions or, subsequently, ensuring that the compression mechanism comes to a standstill in the suction phase occurs in correspondingly precise manner.

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be explained in greater detail using exemplary embodiments. The drawings are meant as examples, and while they are intended to present the idea of the invention, they are not intended to restrict it or, particularly, to conclusively reproduce it.

In this regard, the figures show:

FIG. 1 a schematic representation of a piston refrigerant compressor in a refrigerant circuit according to the state of the art,

FIG. 2 a schematic view of a compression mechanism according to the state of the art,

FIG. 3 a diagram relating to the load torque progression and the operating torque progression over the crank angle in the case of a piston refrigerant compressor according to the state of the art, wherein for reasons of clarity, the load torque and the operating torque are scaled differently,

FIG. 4 a rotational speed progression with a stopping process of a refrigerant compressor of a system according to the invention,

FIG. 5 a rotational speed progression with a stopping process of the refrigerant compressor of a second embodiment of the system according to the invention,

FIG. 6 a rotational speed progression with a stopping process of the refrigerant compressor of a third embodiment of the system according to the invention.

WAYS OF IMPLEMENTING THE INVENTION

FIG. 1 shows a schematic representation of a piston refrigerant compressor 1 connected with an electric power supply 12 and regulated by way of an electronic control device 13, in a coolant circuit that is known, having a condenser 2, a throttle apparatus 3, as well as an evaporator 4. The refrigerant absorbs heat from a refrigeration chamber the evaporator 4, and thereby this chamber is cooled. The evaporated refrigerant compressed by way of a compression mechanism 5 of the piston refrigerant compressor 1, to a higher temperature, and subsequently liquefied in the condenser 2 again, and finally passed back to the evaporator 4 of the refrigeration chamber by way of the throttle apparatus 3.

In FIG. 1 electronic control device 13 of the refrigerant compressor 1 communicates with an electronic control device 14 of a refrigerator 15. However, such a communication possibility is not viewed as being essential to the invention, because it is also conceivable that the electronic control device 13 communicates with a refrigerator 15, which itself does not have its own electronic control device but rather merely a thermostat.

FIG. 2 shows a schematic view of the compression mechanism 5, consisting of a crankshaft 6 driven by means of a drive unit 16, a connecting rod 7, as well as a piston 9 that can move up and down in a cylinder block 8. The compression mechanism 5 is mounted in a housing 11 by way of spring elements 10, which spring elements 10 absorb and are supposed to equalize the vibrations of the unit consisting of compression mechanism 5 and drive unit 16, which vibrations occur on the basis of the rotation of the crankshaft 6 as well as the movements of the piston 9.

The drive unit 16 controlled by the electronic control device 13 is a variable rotational speed drive unit 16, typically a brushless direct-current motor, the rotational speed ω of which can be regulated by means of the electronic control device 13. Capture of the actual rotational speed, which is required for regulation of the rotational speed ω, takes place by means of detection of the counter-voltage induced in a motor coil of the drive unit 16 (induction counter-voltage), so that no further sensors are required, and thereby also the actual rotational velocity is detected. However, it should be noted that the electronic control device 13 according to the invention can, of course, also work together with separate sensors for rotational velocity measurement or rotational speed measurement, such as with Hall sensors, for example.

During the operating duration of a variable rotational speed piston refrigerant compressor 1, fundamentally three phases should be differentiated:

• • the starting phase,
  • the normal, regulated operating phase,
  • the stopping process.

The basis is formed by a refrigeration chamber temperature that can be preselected by the user of a refrigerator 15, within limits (=target temperature), of the refrigerator 15. If one proceeds from a refrigeration chamber that has been cooled to the target temperature, and the refrigerator 15 is being filled or if the refrigerator door is opened, warm air flows into the refrigeration chamber. The electronic control device 14 of the refrigerator 15 detects that the refrigeration chamber temperature is increasing and sends a signal (in general a frequency signal) to the electronic control device 13 of the refrigerant compressor 1, with which signal the device is informed that refrigeration power is required, whereupon the device controls and regulates the refrigerant compressor 1 in accordance with its programming, so as to deliver (more or less) refrigeration output.

In the present example, the electronic control device 13 of the refrigerant compressor 1 will start the compressor so as to compress the refrigerant and extract, heat from the refrigeration chamber, and to reach the target temperature once again. This “turn-on” initiates the starting phase. In this regard, the refrigerant compressor 1, in concrete terms its drive unit 16, is accelerated to a specific rotational speed ω predetermined by the electronic control device 13 of the refrigerant compressor 1. Reaching this rotational speed to ends the starting phase. At this point in time, the target temperature has generally not yet been reached.

The refrigerant compressor 1 then makes a transition into the normal, regulated operating phase. This phase continues as long as the refrigerant compressor 1 is turned on, or, to formulate it somewhat more technically, as long as energy is being provided to the refrigerant by way of the compression mechanism 5, and the drive unit 16 of the refrigerant compressor 1 is generating an operating torque B_m. The compression mechanism 5 can rotate at different rotational speeds ω during this normal, regulated operating phase, depending on whether more or less heat is supposed to be extracted from the refrigeration chamber. For example, if the door of the refrigerator 15 is opened during such a normal, regulated operating phase, then the electronic control device 14 of the refrigerator 15 will demand more refrigeration output from the refrigerant compressor 1 on the basis of the warm air flowing in, so that the electronic control device 13 of the refrigerant compressor 1 increases the rotational speed o of the drive unit 16 and thereby of the compression mechanism 5, so as to be able to transport away the heat that flows into the refrigeration chamber.

The increase in the rotational speed ω is connected with an increased energy demand of the refrigerant compressor 1. When the electronic control device 14 of the refrigerator 15 recognizes that the current refrigeration chamber temperature is approaching the target temperature, the electronic control device 14 of the refrigerator 15 will send a corresponding signal to the electronic control device 13 of the refrigerant compressor 1, so as to demand less refrigeration output and not “overshoot” the target temperature and to approach it slowly The electronic control device 13 of the refrigerant compressor 1 in turn will reduce the rotational speed o of the drive unit 16 /of the compression mechanism 5 on the basis of this demand.

When the electronic control device 14 of the refrigerator 15 recognizes that in the meantime, the refrigeration chamber temperature is increasing again, for example because the refrigeration chamber was refilled, then the electronic control device 14 of the refrigerator 15 will demand more refrigeration output from the electronic control device 13 of the refrigerant compressor 1 once again, so that this device will again increase the rotational speed ω of the drive unit 16/of the compression mechanism 5.

If, after a correspondingly lasting normal, regulated operating phase, the target temperature has been reached, the electronic control device 14 of the refrigerator 15 sends a signal to the electronic control device 13 of the refrigerant compressor 1, with which this device is informed that the target temperature has been reached. Thereupon the electronic control device 13 of the refrigerant compressor 1 shuts off the drive unit 16. Shutting the drive unit 16 off leads to the result that the compression mechanism 5, including the drive unit 16, is in a drive-free state and only continues to rotate on the basis of mass inertia, until the rotational speed co or the rotational velocity is 0. Colloquially, one could also say that the refrigerant compressor 1 “is running down.”

During operation of the compression mechanism 5, impacts exerted on the compression mechanism 5 by the load torque L_m during the compression phase occur, which repeat with every crankshaft revolution and, at low rotational speeds ω, can coincide with the inherent frequency of the oscillation system formed by the spring elements 10, whereby their deflection increases to such an extent that contact can come about of the unit consisting of compression mechanism 5 and drive unit 16 with the housing 11, and thereby undesired noise emissions are generated.

Furthermore, a reversal of the rotational direction of the compression mechanism 5 can come about during the stopping process, when the drive unit 16 is no longer producing any—neither positive nor negative—operating torque B_m, and thereby an additional impact on the compression mechanism 5 is exerted, which also results in an undesired strong deflection of the spring elements 10, with the result that due to this reversal of the rotational direction, the risk also exists that the unit consisting of compression mechanism 5 and drive unit 16 is brought in contact with the housing 11 and causes noise emissions.

In summary, it can be stated that low rotational speeds ω, independent of whether the refrigerant compressor 1 is in the starting phase, the normal, regulated operating phase or in the stopping process, always contain the risk that the oscillation system formed by the spring elements 10 will be excited in the range of its inherent frequency, and therefore contact between the unit consisting of compression mechanism 5 and drive unit 16, and the housing 11 will come about, causing noise as described.

FIG. 3 shows a diagram of the progression of the load torque L_m (dot-dash line in FIG. 3) over the crank angle Φ during a normal, regulated operating phase of a piston refrigerant compressor 1 known from the state of the art, the drive unit 16 of which drives the compression mechanism 5 with an operating torque B_m (broken line in FIG. 3). In this regard, it was assumed that the crankshaft 6 rotates clockwise. The rotational direction therefore takes place from 0° (top dead center (TDC)) to 360° (once again top dead center (TDC)). Furthermore, it should be pointed out that for reasons of clarity, the load torque L_m and the operating torque B_m are scaled differently in FIG. 3.

As is evident from the diagram, the load torque L_m is greatest, in terms of amount, shortly before the piston 9 reaches the top dead center in the compression phase., in other words at approximately 330°, and counteracts the operating torque B_m. At the beginning of the suction phase, in other words at approximately 10° in the present case, the load torque L_m acts in the same rotational direction as the operating torque B_m, i.e. the load torque L_m actually supports the rotation of the compression mechanism 5 in this section of the suction phase (re-expansion phase).

To prevent a stop jolt and the accompanying noise emissions, without a braking torque having to be actively applied for this purpose, it is provided, according to the invention, in the case of a system composed of refrigerant compressor 1 and related electronic control device 13, that the electronic control device 13 is set up for carrying out a method according to the invention for operation of the refrigerant compressor 1, namely for the purpose of

• • when the drive unit 16 is shut off, determining an energy evaluation variable difference W, which is proportional to the energy required for performing one crankshaft revolution,
  • at a measurement rotational speed ω, determining an energy evaluation variable E(ω), which is proportional to a rotational energy at the measurement rotational speed ω, along with the number N of the crankshaft revolutions remaining until standstill of the compression mechanism 5 when the drive unit 16 is shut off,
  • checking whether the remaining crankshaft revolutions N at shut-off of the drive unit 16 allow stopping of the compression mechanism 5 in its suction phase at a reference piston position,
  • if applicable, turning the drive unit 16 on and, taking into consideration the energy evaluation variable difference W, determining a shut-off rotational speed ω_shut-off, at which the drive unit 16 must be shut off at the reference piston position so as to bring about a standstill of the compression mechanism 5 in the suction phase, and turning the drive unit 16 off at the shut-off rotational speed ω_shut-off,
  • or, if necessary, turning the drive unit 16 on and operating it at a limit rotational speed ω_limit that can be predetermined, and, taking into consideration. the energy evaluation variable difference W, determining a shut-off piston position and turning the drive unit 16 off at the limit rotational speed ω_limit and the shut-off piston position.

In the following, three embodiment variants of the system or method according to the invention are explained in greater detail, using diagrams of the rotational speed ω as a function of time t. In this regard, the control device 13 is set up, in each instance, for the purpose of

• • determining the energy evaluation variable difference W by means of formation of the difference of the energy evaluation variables E(ω₁), E(ω₂) in the case of two consecutive revolutions of the crankshaft 6, so as to be able to determine, by means of formation of the quotient N=W(ω)/W, how many revolutions N the drive-free compression mechanism 5 can continue to run, proceeding from the measurement rotational speed ω and the reference piston position, wherein it can be determined, on the basis of the post-decimal portion of the number of revolutions N that are determined, whether the compression mechanism 5 would come to a standstill in the suction phase or in the compression phase,
  • and, using quotient formation and taking into consideration the post-decimal portion of the determined number of revolutions N, driving the compression mechanism 5 in such a manner, and turning the drive unit 16 off in such a manner that the compression mechanism 5 comes to a standstill during the suction phase.

In the exemplary embodiments shown, the reference piston position is the top dead center (TDC) of the piston 9 in the cylinder 8.

Furthermore, in the exemplary embodiments shown, the energy evaluation variable E(ω) for the measurement rotational speed ω is calculated or determined by means of squaring the measurement rotational speed ω, i.e.

E(ω)=ω².

In the case of the first embodiment variant, the control device 13 is set up for driving the compression mechanism 5 in such a manner that the shut-off rotational speed ω_shut-off is reached, and for shutting the drive unit 16 off at the shut-off rotational speed ω_shut-off and the reference piston position, wherein the shut-off rotational speed ω_shut-off is determined in that

• • the energy evaluation variable E(ω_b) is determined at a determination rotational speed ω_b that functions as the measurement rotational speed, which is present when the drive unit 16 is shut off to determine the energy evaluation variable difference,
  • the number of revolutions N is calculated by means of quotient formation:

N=E(ω_b)/W,

• • an adapted number of revolutions N′ is calculated, in that the number of revolutions N is rounded up to the next greater whole number, and subsequently, an adapt _ion number in the range of 0.1 to 0.4, preferably of 0.2

to 0.3, added, and

• • the shut-off rotational speed ω_shut-off is calculated as the root of the product of the adapted number of revolutions N′ and the energy evaluation variable difference W:

ω_shut-off=(N′*W)^0.5.

FIG. 4 shows the diagram that results from the rotational speed ω over the time t for an application case in which the refrigerant compressor 1 is first operated at a specific rotational speed ω₀. for example 2000 min⁻¹. To determine the energy evaluation variable difference W, the drive unit 16 is turned off, so that the compression mechanism 5 continues to run in drive free manner. Now, the related energy evaluation variables are calculated for two consecutive crankshaft revolutions having the rotational speeds ω₁ and ω₂:

E(ω₁)=ω₁² and E(ω₂)=ω₂².

Or the energy evaluation variable difference W=ω₁²−ω₂² is obtained immediately.

The compression mechanism continues to run down until the determination rotational speed ω_b is reached, at which the compression mechanism 5 is operated. by means of the turned-on drive unit 16, and at which the energy evaluation variable E(ω_b)=ω_b² is calculated.

Then the number of revolutions N=ω_b²/(ω₁²−ω₂²) or the adapted number of revolutions N′ is calculated, and according to the above formula, the shut-off rotational speed ω_shut-off is calculated, which is greater in the example shown in FIG. 4 than the determination rotational speed ω_b. Accordingly, it can be seen in FIG. 4 that the compression mechanism 5 is accelerated to the shut-off rotational speed ω_shut-off by means of the drive unit 16. When this speed is set, the drive unit 16 is turned off as soon as the reference piston position (TDC) has been reached. The compression mechanism 5 then runs down to rotational speed zero and comes to a standstill in the suction phase.

In the case of the second embodiment variant, the control device 13 is set up for

a) shutting the drive unit 16 off and

b) while the drive unit 16 is shut off,

b1) determining the energy evaluation variable difference W,

b2) determining the energy evaluation variable E(ω_run-down) for a run-down rotational speed ω_run-down that is then present and functions as the measurement rotational speed,

b3) calculating the number of revolutions N by means of quotient formation:

N=E(ω_tun-down)/W

b4) and comparing the post-decimal portion of the number of revolutions N with an adaptation number in the range of 0.1 to 0.4, preferably of 0.2 to 0.3, and

c) if the post-decimal portion is greater than the adaptation number, driving the compression mechanism 5 only for the duration of part of a complete revolution of the crankshaft 6.

FIG. 5 shows the related diagram of rotational speed ω versus time t, once again for an application case in which the refrigerant compressor 1 is first operated at a specific rotational speed ω₀, for example 2000 min⁻¹. To determine the energy evaluation variable difference W, the drive unit 16 is shut off, so that the compression mechanism 5 continues to run in drive-free manner. Now the related energy evaluation variables are calculated for two consecutive crankshaft revolutions at the rotational speeds ω₁ and ω₂:

E(107 ₁)=ω₁² and E(ω₂)=ω₂².

Or the energy evaluation variable difference W=ω₁²−ω₂² is obtained immediately. This calculation takes place practically instantaneously, so that the run-down rotational speed ω_run-down now present is equal to ω₂, so that it holds true that E(ω_run-down=E(ω₂)=ω₂². Now the rotational speed number N=E(ω_run-down/W can be calculated.

On the basis of the comparison of the post-decimal portion of N with the adaptation number, the drive unit 16 is turned on for a moment, during which only part of a complete revolution of the crankshaft 6 takes place, so as to more or less “give” the compression mechanism 5 “a shove.” Accordingly, the rotational speed ω increases slightly for a short time (in FIG. 5, shown by way of a time span not shown to scale, for reasons of clarity). Then the compression mechanism 5 runs down to rotational speed zero and comes to a standstill in the suction phase.

In the case of the third embodiment variant, the control device 13 is set up for driving the compression mechanism 5 in such a manner that the limit rotational speed ω_limit is reached, and shutting the drive unit 16 off at the limit rotational speed ω_limit and the shut-off piston position, wherein the shut-off piston position is determined in that

• • the energy evaluation variable E(ω_limit) is determined at the limit rotational speed ω_limit,
  • the number of revolutions N is calculated by means of quotient formation:

N=E(ω_limit)/W,

• • the post-decimal portion of the number of revolutions N is determined,
  • an adapted post-decimal portion is determined in that an adaptation number in the range of 0.1 to 0.4, preferably of 0.2 to 0.3, is subtracted from the post-decimal portion of the number of revolutions N,
  • the adapted post-decimal portion is converted to a piston position, and. this position is deducted from the reference piston position (TDC).

FIG. 6 shows the resulting diagram of rotational speed ω over the time t for an application case in which the refrigerant compressor 1 is first operated at a specific rotational speed ω₀, for example 2000 min⁻¹. To determine the energy evaluation variable difference W, the drive unit 16 is shut off, so that the compression mechanism 5 continues to run in drive-free manner. Now the related energy evaluation variables are calculated for two consecutive crankshaft revolutions at the rotational speeds ω₁ and ω₂:

E(ω₁)=ω₁² and E(ω₂)=ω₂².

Or the energy evaluation variable difference W=ω₁²−ω₂² is obtained immediately. Furthermore, as described above, the number of revolutions N or their post-decimal portion is determined and the piston position is determined, which is deducted from the reference piston position so as to obtain the shut-off piston position, by means of subtraction of the adaptation number from the post-decimal portion.

In contrast to the case of the first embodiment variant shown in FIG. 4, the compression mechanism 5 now runs down to the limit rotational speed ω_limit and is then held at the limit rotational speed ω_limit by means of the drive unit 16. However, it would of course also be conceivable that after determination of the energy evaluation variable difference W, the compression mechanism 5 is brought to the limit rotational speed 107 _limit with the drive device 16 turned on, and held there. However, holding at the limit rotational speed w limit takes place only very briefly or for a moment, as is shown in exaggerated manner in FIG. 6 for reasons of clarity, namely for the time required to reach the shut-off piston position. As soon as the shut-off piston position has been reached, the drive unit 16 is shut off with final effect, and the compression mechanism 5 runs down to a standstill, wherein the compression mechanism 5 comes to a standstill in the suction phase.

REFERENCE SYMBOL LIST

1 refrigerant compressor

2 condenser

3 throttle apparatus

4 evaporator

5 compression mechanism

6 crankshaft

7 connecting rod

8 cylinder block

9 piston

10 spring elements

11 housing

12 power supply

13 electronic control device of the refrigerant compressor

14 electronic control device of the refrigerator

15 refrigerator

16 drive unit

B_m operating torque

L_m load torque

Φ crank angle or rotation angle

t time

E energy evaluation variable

W energy evaluation variable difference

ω (measurement) rotational speed

N number of revolutions

N′ adapted number of revolutions

ω_shut-off shut-off rotational speed

ω_limit limit rotational speed

ω_b determination rotational speed

ω_run-down run-down rotational speed

Claims

1-30 (canceled)

31. A system comprising a refrigerant compressor and an electronic control device (13) for the refrigerant compressor (1), which refrigerant compressor (1) at least comprises

a drive unit (16),

a compression mechanism (5) standing in an active connection with a rotor of the drive unit (16), having at least a piston (9) that can move back and forth in a cylinder of a cylinder block (8) and can be driven by way of a crankshaft (6), so as to cyclically draw refrigerant into the cylinder during a suction phase and compress the refrigerant in the cylinder during a compression phase that follows the suction phase,

wherein the electronic control device (13) is set up for

capturing and controlling and/or regulating a rotational speed (ω) of the crankshaft (6),

at least approximately capturing a piston position of the piston (9),

wherein the electronic control device (13) is set up for

when the drive unit (16) is shut off, determining an energy evaluation variable difference (W) that is proportional to the energy required for performing one crankshaft revolution,

at a measurement rotational speed (ω), determining an energy evaluation variable (E(ω)), which is proportional to the rotational energy at the measurement rotational speed (ω), as well determining the number of crankshaft revolutions (N) remaining until standstill of the compression mechanism (5) when the drive unit (16) is shut off,

checking whether the remaining crankshaft revolutions (N) at shut-off of the drive unit (16) at a reference piston position allow stopping of the compression mechanism (5) in its suction phase,

if necessary, turning the drive unit (16) on and, taking into consideration the energy evaluation variable difference (W), determining a shut-off rotational speed (ωshut-off), at which the drive unit (16) should be shut off at the reference piston position, so as to bring about a standstill of the compression mechanism (5) in the suction phase and to shut off the drive unit (16) at the shut-off rotational speed (ωshut-off),

or, if necessary, turning the drive unit (16) on and operating it at a limit rotational speed (ωlimit) that can be predetermined, and, taking into consideration the energy evaluation variable difference (W), determining a shut-off piston position and shutting off the drive unit (16) at the limit rotational speed (ωlimit) and the shut-off piston position.

32. The system according to claim 31, wherein the control device (13) is set up for

determining the energy evaluation variable difference (W) by means of formation of the difference of the energy evaluation variables (E(ω1), E(ω2)) at two consecutive revolutions of the crankshaft (6), so as to be able to determine, by means of formation of the quotient of energy evaluation variable/energy evaluation variable difference (E(ω)/W), how many revolutions (N; N=E(ω)/W) the drive-free compression mechanism (5) can continue to run, proceeding from the measurement rotational speed (ω) and the reference piston position, wherein based on the post-decimal portion of the determined number of revolutions (N), it can be determined whether the compression mechanism (5) would come to a standstill in the suction phase or in the compression phase,

and, using the quotient formation and taking into consideration the post-decimal portion of the determined number of revolutions (N), driving the compression mechanism (5) in such a manner and shutting off the drive unit (16) in such a manner that the compression mechanism (5) comes to a standstill during the suction phase.

33. The system according to claim 31, wherein the control device (13) is set up for shutting off the drive unit (16) and determining the energy evaluation variable difference (W) only when the rotational speed (ω) is greater than or equal to a minimum rotational speed (ωmin), preferably one that can be predetermined.

34. The system according to claim 31, wherein the reference piston position is the top dead center of the piston (9) in the cylinder (8).

35. The system according to claim 31, wherein the electronic control device (13) is set up for driving the compression mechanism (5) in such a manner that the shut-off rotational speed (ωshut-off) is reached, and shutting off the drive unit (16) at the shut-off rotational speed (ωshut-off) and the reference piston position, wherein the shut-off rotational speed (ωshut-off) is determined in that

the energy evaluation variable (E(ωb)) is determined at a determination rotational speed (ωb) that functions as a measurement rotational speed, which is preferably present when the drive unit (16) is shut off to determine the energy evaluation variable difference (W),

the number of revolutions (N) is calculated by means of quotient formation: N=E(ωb)/W,

an adapted number of revolutions (N′) is calculated, in that the number of revolutions (N) is rounded up to the next greater whole number, and subsequently, an adaptation number between 0 and 1 is added, and

the shut-off rotational speed (ωshut-off) is calculated within a constant factor (c), as the root of the product of the adapted number of revolutions (N′) and the energy evaluation variable difference (W): ωshut-off=c*(N′*W)0.5.

36. The system according to claim 35, wherein the adaptation number lies in the range of 0.1 to 0.4, preferably of 0.2 to 0.3, and wherein the reference piston position is the top dead center of the piston (9) in the cylinder (8).

37. The system according to claim 31, wherein the electronic control device (13) is set up for driving the compression mechanism (5) in such a manner that the limit rotational speed (ωlimit) is reached, and shutting off the drive unit (16) at the limit rotational speed (ωlimit) and the shut-off piston position, wherein the shut-off piston position is determined in that

the energy evaluation variable (E(ωlimit)) is determined at the limit rotational speed (ωlimit),

the number of revolutions (N) is calculated by means of quotient formation: N=E(ωlimit)/W,

the post-decimal portion of the number of revolutions (N) is determined,

an adapted post-decimal portion is determined in that an adaptation number between 0 and 1 is subtracted from the post-decimal portion of the number of revolutions (N),

the adapted post-decimal portion is converted to a piston position and this is deducted from the reference piston position.

38. The system according to claim 37, wherein the adaptation number lies in the range of 0.1 to 0.4, preferably of 0.2 to 0.3, and wherein the reference piston position is the top dead center of the piston (9) in the cylinder (8).

39. The system according to claim 31, wherein the electronic control device (13) is set up for

a) shutting off the drive unit (16) and

b) when the drive unit (16) is shut off,

b1) determining the energy evaluation variable difference (W),

b2) determining the energy evaluation variable (E(ωrun-down)) for a run-down rotational speed (ωrun-down) that is then present and functions as a measurement rotational speed,

b3) calculating the number of revolutions (N) by means of quotient formation: N=E (ωrun-down)/W,

b4) and comparing the post-decimal portion of the number of revolutions (N) with an adaptation number between 0 and 1, and

c) if the post-decimal portion is greater than the adaptation number, driving the compression mechanism (5) only for the duration of part of a complete revolution of the crankshaft (6).

40. The system according to claim 39, wherein the electronic control device (13) is set up for iteratively repeating at least the steps b2), b3), b4), and c).

41. The system according to claim 39, wherein the adaptation number lies in the range of 0.1 to 0.4, preferably of 0.2 to 0.3, and wherein the reference piston position is the top dead center of the piston (9) in the cylinder (8).

42. The system according to claim 31, wherein the electronic control device (13) is set up for determining the energy evaluation variable (E(ω)) for the measurement rotational speed (ω) by means of squaring the measurement rotational speed (ω).

43. The system according to claim 32, wherein the control device (13) is set up for determining the energy evaluation variable difference (W) in such a manner that multiple energy evaluation variable differences (W) are determined for rotational speeds (ω1, ωi+1) at two consecutive revolutions, in each instance, in a sequence of more than two consecutive revolutions, and an average value is formed from these energy evaluation variable differences (W).

44. A method for operation of a refrigerant compressor having a drive unit (16), a compression mechanism (5) that can be driven by means of the drive unit (16), comprising a piston (9) as well as a crankshaft (6) that stands in connection with the latter by way of a connecting rod, characterized in that the method comprises the following steps:

when the drive unit (16) is shut off, determining an energy evaluation variable difference (W), which is proportional to the energy required for performing one crankshaft revolution,

at a measurement rotational speed (ω), determining an energy evaluation variable (E(ω)), which is proportional to a rotational energy at the measurement rotational speed (ω), and calculating the number (N) of crankshaft revolutions remaining when the drive unit (16) is shut off, until a standstill of the compression mechanism occurs,

checking whether the remaining crankshaft revolutions (N) at shut-off of the drive unit (16) at a reference piston position allow stopping of the compression mechanism (5) in its suction phase,

if necessary, turning on the drive unit (16) and, taking into consideration the energy evaluation variable difference (W), determining a shut-off rotational speed (ωshut-off), at which the drive unit (16) must be shut off at the reference piston position, so as to bring about a standstill of the compression mechanism (5) in the suction phase and shut-off of the drive unit (16) at the shut-off rotational speed (ωshut-off),

or, if necessary, turning on the drive unit (16) and operating the same at a limit rotational speed (ωlimit) that can be predetermined and, taking into consideration the energy evaluation variable difference (W), determining a shut-off piston position and shut-off of the drive unit (16) at the limit rotational speed (ωlimit) and at the shut-off piston position.

45. The method according to claim 44, wherein

the energy evaluation variable difference (W) is determined by means of formation of the difference of the energy evaluation variables (E(ω1), E(ω2)) at two consecutive revolutions of the crankshaft (6),

by means of formation of the quotient of energy evaluation variable/energy evaluation variable difference (E(ω)/W), it is determined how many revolutions (N; N=E(ω)/W) the drive-free compression mechanism (5) can continue to run, proceeding from the measurement rotational speed (ω) and the reference piston position, wherein it is determined, on the basis of the post-decimal portion of the determined number of revolutions (N), whether the compression mechanism (5) would come to a standstill in the suction phase or in the compression phase,

using the quotient formation and taking into consideration the post-decimal portion of the determined number of revolutions (N), the compression mechanism (5) is driven in such a manner, and the drive unit (16) is shut off in such a manner that the compression mechanism (5) comes to a standstill during the suction phase.