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.

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 () 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 (), determining an energy evaluation variable (E()), which is proportional to the rotational energy at the measurement rotational speed (), 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 (.sub.shut-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 (.sub.shut-off), or, if necessary, turning the drive unit (16) on and operating it at a limit rotational speed (.sub.limit) 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 (.sub.limit) 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(.sub.1), E(.sub.2)) 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()/W), how many revolutions (N; N=E()/W) the drive-free compression mechanism (5) can continue to run, proceeding from the measurement rotational speed () 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 () is greater than or equal to a minimum rotational speed (.sub.min), 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 (.sub.shut-off) is reached, and shutting off the drive unit (16) at the shut-off rotational speed (.sub.shut-off) and the reference piston position, wherein the shut-off rotational speed (.sub.shut-off) is determined in that the energy evaluation variable (E(.sub.b)) is determined at a determination rotational speed (.sub.b) 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(.sub.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 adaptation number between 0 and 1 is added, and the shut-off rotational speed (.sub.shut-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):
.sub.shut-off=c*(N*W).sup.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 (.sub.limit) is reached, and shutting off the drive unit (16) at the limit rotational speed (.sub.limit) and the shut-off piston position, wherein the shut-off piston position is determined in that the energy evaluation variable (E(.sub.limit)) is determined at the limit rotational speed (.sub.limit), the number of revolutions (N) is calculated by means of quotient formation: N=E(.sub.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 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(.sub.run-down)) for a run-down rotational speed (.sub.run-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 (.sub.run-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()) for the measurement rotational speed () by means of squaring the measurement rotational speed ().

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 (.sub.1, .sub.i+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 (), determining an energy evaluation variable (E()), which is proportional to a rotational energy at the measurement rotational speed (), 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 (.sub.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 shut-off of the drive unit (16) at the shut-off rotational speed (.sub.shut-off), or, if necessary, turning on the drive unit (16) and operating the same at a limit rotational speed (.sub.limit) 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 (.sub.limit) 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(.sub.1), E(.sub.2)) at two consecutive revolutions of the crankshaft (6), by means of formation of the quotient of energy evaluation variable/energy evaluation variable difference (E()/W), it is determined how many revolutions (N; N=E()/W) the drive-free compression mechanism (5) 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 (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.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0099] 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.

[0100] In this regard, the figures show:

[0101] FIG. 1 a schematic representation of a piston refrigerant compressor in a refrigerant circuit according to the state of the art,

[0102] FIG. 2 a schematic view of a compression mechanism according to the state of the art,

[0103] 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,

[0104] FIG. 4 a rotational speed progression with a stopping process of a refrigerant compressor of a system according to the invention,

[0105] 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,

[0106] 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

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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 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 , 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.

[0111] During the operating duration of a variable rotational speed piston refrigerant compressor 1, fundamentally three phases should be differentiated: [0112] the starting phase, [0113] the normal, regulated operating phase, [0114] the stopping process.

[0115] 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.

[0116] 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 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.

[0117] 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.sub.m. The compression mechanism 5 can rotate at different rotational speeds 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.

[0118] The increase in the rotational speed 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.

[0119] 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 of the drive unit 16/of the compression mechanism 5.

[0120] 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.

[0121] During operation of the compression mechanism 5, impacts exerted on the compression mechanism 5 by the load torque L.sub.m during the compression phase occur, which repeat with every crankshaft revolution and, at low rotational speeds , 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.

[0122] 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 anyneither positive nor negativeoperating torque B.sub.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.

[0123] In summary, it can be stated that low rotational speeds , 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.

[0124] FIG. 3 shows a diagram of the progression of the load torque L.sub.m (dot-dash line in FIG. 3) over the crank angle 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.sub.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.sub.m and the operating torque B.sub.m are scaled differently in FIG. 3.

[0125] As is evident from the diagram, the load torque L.sub.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.sub.m. At the beginning of the suction phase, in other words at approximately 10 in the present case, the load torque L.sub.m acts in the same rotational direction as the operating torque B.sub.m, i.e. the load torque L.sub.m actually supports the rotation of the compression mechanism 5 in this section of the suction phase (re-expansion phase).

[0126] 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 [0127] 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, [0128] at a measurement rotational speed , determining an energy evaluation variable E(), which is proportional to a rotational energy at the measurement rotational speed , 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, [0129] 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, [0130] if applicable, turning the drive unit 16 on and, taking into consideration the energy evaluation variable difference W, determining a shut-off rotational speed .sub.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 .sub.shut-off, [0131] or, if necessary, turning the drive unit 16 on and operating it at a limit rotational speed .sub.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 .sub.limit and the shut-off piston position.

[0132] 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 as a function of time t. In this regard, the control device 13 is set up, in each instance, for the purpose of [0133] determining the energy evaluation variable difference W by means of formation of the difference of the energy evaluation variables E(.sub.1), E(.sub.2) 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()/W, how many revolutions N the drive-free compression mechanism 5 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 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, [0134] 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.

[0135] In the exemplary embodiments shown, the reference piston position is the top dead center (TDC) of the piston 9 in the cylinder 8.

[0136] Furthermore, in the exemplary embodiments shown, the energy evaluation variable E() for the measurement rotational speed is calculated or determined by means of squaring the measurement rotational speed , i.e.

E()=.sup.2.

[0137] 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 .sub.shut-off is reached, and for shutting the drive unit 16 off at the shut-off rotational speed .sub.shut-off and the reference piston position, wherein the shut-off rotational speed .sub.shut-off is determined in that [0138] the energy evaluation variable E(.sub.b) is determined at a determination rotational speed .sub.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, [0139] the number of revolutions N is calculated by means of quotient formation:

N=E(.sub.b)/W, [0140] 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

[0141] to 0.3, added, and [0142] the shut-off rotational speed .sub.shut-off is calculated as the root of the product of the adapted number of revolutions N and the energy evaluation variable difference W:

.sub.shut-off=(N*W).sup.0.5.

[0143] FIG. 4 shows the diagram that results from the rotational speed over the time t for an application case in which the refrigerant compressor 1 is first operated at a specific rotational speed .sub.0. for example 2000 min.sup.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 .sub.1 and .sub.2:

E(.sub.1)=.sub.1.sup.2 and E(.sub.2)=.sub.2.sup.2.

[0144] Or the energy evaluation variable difference W=.sub.1.sup.2.sub.2.sup.2 is obtained immediately.

[0145] The compression mechanism continues to run down until the determination rotational speed .sub.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(.sub.b)=.sub.b.sup.2 is calculated.

[0146] Then the number of revolutions N=.sub.b.sup.2/(.sub.1.sup.2.sub.2.sup.2) or the adapted number of revolutions N is calculated, and according to the above formula, the shut-off rotational speed .sub.shut-off is calculated, which is greater in the example shown in FIG. 4 than the determination rotational speed .sub.b. Accordingly, it can be seen in FIG. 4 that the compression mechanism 5 is accelerated to the shut-off rotational speed .sub.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.

[0147] In the case of the second embodiment variant, the control device 13 is set up for

[0148] a) shutting the drive unit 16 off and

[0149] b) while the drive unit 16 is shut off,

[0150] b1) determining the energy evaluation variable difference W,

[0151] b2) determining the energy evaluation variable E(.sub.run-down) for a run-down rotational speed .sub.run-down that is then present and functions as the measurement rotational speed,

[0152] b3) calculating the number of revolutions N by means of quotient formation:

N=E(.sub.tun-down)/W

[0153] 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

[0154] 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.

[0155] FIG. 5 shows the related diagram of rotational speed versus time t, once again for an application case in which the refrigerant compressor 1 is first operated at a specific rotational speed .sub.0, for example 2000 min.sup.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 .sub.1 and .sub.2:

E(107 .sub.1)=.sub.1.sup.2 and E(.sub.2)=.sub.2.sup.2.

[0156] Or the energy evaluation variable difference W=.sub.1.sup.2.sub.2.sup.2 is obtained immediately. This calculation takes place practically instantaneously, so that the run-down rotational speed .sub.run-down now present is equal to .sub.2, so that it holds true that E(.sub.run-down=E(.sub.2)=.sub.2.sup.2. Now the rotational speed number N=E(.sub.run-down/W can be calculated.

[0157] 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 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.

[0158] 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 .sub.limit is reached, and shutting the drive unit 16 off at the limit rotational speed .sub.limit and the shut-off piston position, wherein the shut-off piston position is determined in that [0159] the energy evaluation variable E(.sub.limit) is determined at the limit rotational speed .sub.limit, [0160] the number of revolutions N is calculated by means of quotient formation:

N=E(.sub.limit)/W, [0161] the post-decimal portion of the number of revolutions N is determined, [0162] 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, [0163] the adapted post-decimal portion is converted to a piston position, and. this position is deducted from the reference piston position (TDC).

[0164] FIG. 6 shows the resulting diagram of rotational speed over the time t for an application case in which the refrigerant compressor 1 is first operated at a specific rotational speed .sub.0, for example 2000 min.sup.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 .sub.1 and .sub.2:

E(.sub.1)=.sub.1.sup.2 and E(.sub.2)=.sub.2.sup.2.

[0165] Or the energy evaluation variable difference W=.sub.1.sup.2.sub.2.sup.2 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.

[0166] 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 .sub.limit and is then held at the limit rotational speed .sub.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 .sub.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

[0167] 1 refrigerant compressor

[0168] 2 condenser

[0169] 3 throttle apparatus

[0170] 4 evaporator

[0171] 5 compression mechanism

[0172] 6 crankshaft

[0173] 7 connecting rod

[0174] 8 cylinder block

[0175] 9 piston

[0176] 10 spring elements

[0177] 11 housing

[0178] 12 power supply

[0179] 13 electronic control device of the refrigerant compressor

[0180] 14 electronic control device of the refrigerator

[0181] 15 refrigerator

[0182] 16 drive unit

[0183] B.sub.m operating torque

[0184] L.sub.m load torque

[0185] crank angle or rotation angle

[0186] t time

[0187] E energy evaluation variable

[0188] W energy evaluation variable difference

[0189] (measurement) rotational speed

[0190] N number of revolutions

[0191] N adapted number of revolutions

[0192] .sub.shut-off shut-off rotational speed

[0193] .sub.limit limit rotational speed

[0194] .sub.b determination rotational speed

[0195] .sub.run-down run-down rotational speed