METHOD FOR OPERATING A PISTON COMPRESSOR, AND PISTON COMPRESSOR

Abstract

Piston compressors and methods for operating a piston compressor for a motor vehicle, in particular an air spring piston compressor of an air suspension system or compressed-air sensor cleaning system of the motor vehicle. A compressor piston is driven inside a compressor cylinder, at least indirectly, by a drive shaft of a drive motor rotatable about a rotary axis in at least one rotation direction. A control device of the drive motor reverses the rotation direction of the drive motor when the drive motor is started according to at least one definable rotation direction parameter.

Claims

1. A method for operating a piston compressor for an air spring piston compressor of an air suspension system or compressed-air sensor cleaning system of a motor vehicle, the method comprising: driving a compressor piston inside a compressor cylinder, at least indirectly, by a drive shaft of a drive motor rotatable about a rotary axis in at least one rotation direction; and reversing, via a control device of the drive motor, the rotation direction of the drive motor when the drive motor is started according to at least one definable rotation direction parameter.

2. The method according to claim 1, wherein the definable rotation direction parameter accounts for a useful signal selected from at least one of a number-of-starts signal, a number of revolutions, or an operating time, wherein the useful signal characterizes at least one of a predeterminable number of starts, a predeterminable number of revolutions, or a predeterminable operating time.

3. The method according to claim 1, wherein the definable rotation direction parameter accounts for an event signal.

4. The method according to claim 3, wherein the event signal is a sensor signal, a user signal, or an error signal.

5. The method according to claim 3, wherein the event signal comprises a sensor signal characterizing a mechanical variable and/or an electrical variable.

6. The method according to claim 5, wherein the sensor signal characterizes at least one of a starting current, a drive shaft position at a time of starting the drive motor, or a wear state, wherein the definable rotation direction parameter is determined according to at least one predeterminable threshold value of the sensor signal.

7. The method according to claim 6, wherein the sensor signal for the drive shaft position determines the definable rotation direction parameter in a decompression direction of the compressor cylinder inside the compressor piston.

8. The method according to claim 7, wherein the sensor signal for the drive shaft position is for an angle of the drive shaft.

9. The method according to claim 6, wherein the sensor signal determines the definable rotation direction parameter with regard to a minimized starting current.

10. The method according to claim 6, wherein the sensor signal of the wear state of an operating pressure state or of an operating current behavior determines the definable rotation direction parameter with regard to a minimized wear state.

11. The method according to claim 10, wherein the wear state is an abrasion or friction state.

12. A piston compressor for an air spring compressor of an air suspension system or compressed-air sensor cleaning system of a motor vehicle, the piston compressor comprising: at least one compressor piston movable inside a compressor cylinder, the compressor cylinder being drivable at least indirectly by a drive shaft of a drive motor rotatable about a rotary axis in at least one rotation direction; and at least one control device configured to reverse the rotation direction of the drive motor when the drive motor is started according to at least one definable rotation direction parameter.

13. The piston compressor according to claim 12, wherein the at least one control device comprises a useful signal generating unit and/or an event signal generating unit, the useful signal generating unit and/or the event signal generating unit configured to supply the definable rotation direction parameter for generating a rotation direction actuating current of the drive motor.

14. The piston compressor according to claim 12, wherein the at least one control device comprises a useful signal generating unit having a recorder configured to record at least one of a number of starts, a number of revolutions, or an operating time.

15. The piston compressor according to claim 12, wherein the at least one control device comprises an event signal generating unit having a processor configured to process a sensor signal of one or more of a starting current, an operating current, a drive shaft position, or a wear state.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The drawings depict illustrative examples. The drawings, the description and the claims contain many features in combination. The person skilled in the art will also consider the features individually, and combine them into useful further combinations.

[0006] FIG. 1 depicts a simplified schematic cross-sectional view of an advantageous piston compressor operable in accordance with an embodiment of the method in accordance with one or more aspects shown and described herein, and

[0007] FIG. 2 depicts a simplified flow diagram for explaining an embodiment of an operating method in accordance with the present disclosure.

[0008] Identical elements are denoted with the same reference signs in the figures. The figures show examples and should not be understood as being limiting.

DETAILED DESCRIPTION

[0009] A compressed air-based cleaning of sensors in the region of the vehicle sensor system can serve to increase operability and efficiency in driving operation. Sensors responsible for navigation and awareness of the surroundings, such as LiDAR, radar and cameras, but also windshields and headlights, may be affected by various environmental influences, including dust, dirt and other particles. A compressed air compressor for sensor cleaning can keep the sensors clean and operational, in particular for autonomous vehicle control, by means of compressed air cleaning.

[0010] For that purpose, a piston compressor of this type has as its principal components a compressor piston, movable inside a compressor cylinder for suction and compression of air, which is operatively connected, at least indirectly, and mostly via a connecting rod, to a drive shaft driven by a drive motor, and is hence drivable. The compressor cylinder may be designed both for single-stage operation with one compressor lid and for two-stage operation with two compressor lids opposite one another along the piston.

[0011] In operation of the piston compressor, a driving force is generated by means of the drive motor and transmitted to the drive shaft, the latter being set in rotation. This rotational force is usually converted into a lifting force by means of the connecting rod coupled to the drive shaft and compressor piston, and transmitted to the compressor piston. As a result, the compressor piston is moved up and down inside the compressor housing in a lifting and lowering movement. The compressor housing has an inlet for suction of air out of the atmosphere and an outlet for the sucked-in air, wherein the inlet and outlet are fluidically connected to a piston chamber, inside which the compressor piston is movably mounted, and are often closable by valves, in particular by non-return valves. A negative pressure, by which the air is sucked in, is generated inside the compressor housing or piston chamber by the lowering movement of the compressor piston. The previously sucked-in air is compressed by the subsequent lifting movement, and supplied via the outlet to its destination, for example to the air spring bag or to a compressed air reservoir of a vehicle air spring system or of a sensor cleaning system.

[0012] Generally speaking, piston compressors can be operated reciprocally in respect of a rotation direction of the drive shaft, e.g., both clockwise and counterclockwise. As a rule, a rotation direction of the drive shaft is defined inertially, so that the rotation direction of the drive shaft is fixed over the lifecycle of the piston compressor. To that extent, drive methods for known piston compressors are as a rule designed in terms of their structure and mode of operation such that the respective drive shaft is always rotatable in one and the same rotation direction or always rotates in one rotation direction only, during operation for its intended purpose. As noted, methods of this type for operating the piston compressor lead however to the problem of one-sided stress and wear on the components, and hence sooner or later to a loss of their functionality and service life due to (one-sided) wear. Specifically, one-sided stresses occur at the cylinder wall, the piston lid, the connecting rod bearings and the crankshaft, and are also particularly pronounced at the seal between the compressor piston and the surrounding housing or compressor cylinder.

[0013] To mitigate this problem, conventional methods match the geometry and the material of the piston compressor components to this one-sided stress or to optimize them for this such that a defined minimum service life is attained. This leads to the consequential problem that the design and manufacture of the piston compressor are comparatively demanding and complex, and hence expensive.

[0014] The object of the present disclosure is to provide an improved method for operating piston compressors, where the one-sided wear and stress on the piston compressor components usual with the known methods due to the rotation direction being always the same are at least reduced, and in particular prevented.

[0015] This object is achieved by methods and by a piston compressor according to the claims. Advantageous embodiments of the present disclosure are also disclosed in the claims.

[0016] The present disclosure proceeds from a method for operating a piston compressor for a motor vehicle, in particular an air spring piston compressor of an air suspension system or compressed-air sensor cleaning system of the motor vehicle, wherein at least one compressor piston is driven, at least indirectly, inside a compressor cylinder by a drive shaft of a drive motor rotatable about a rotary axis in at least one rotation direction, in order to compress sucked-in air.

[0017] Driving of the compressor piston by the drive shaft is achieved in particular by a connecting rod (indirect drive).

[0018] In accordance with the present disclosure, it is provided that a control device of the drive motor changes, in particular reverses, the rotation direction of the drive motor when the drive motor is started, depending on at least one definable rotation direction parameter.

[0019] Changing or reversing means, in connection with the present disclosure, above all that rotation is now in the opposite direction, for example from counterclockwise to clockwise rotation. The intention here is not an abrupt change in the rotation direction; instead a rotation direction, changeable at every new start, should be defined whenever the drive shaft is started up for the respective work operation. It is also possible to make a rotation direction change during operation, which should however be achieved by a continuously decreasing speed in one rotation direction until stationary and thereafter by a continuously increasing speed in an opposite rotation direction, so that there is a gentle and stress-minimizing transition when the rotation direction changes.

[0020] In accordance with the present disclosure, the rotation direction is, depending on environmental influences characterized by the rotation direction parameter, adjusted when the drive motor is started or changed again/continuously at every start, such that the one-sided wear and stress on the components of the piston compressor usual with the known methods is prevented. As a result, the rotation direction change in accordance with the present disclosure leads to a selective and uniform stress on the piston compressor. This advantageously maintains the performance of the piston compressor for longer, with its operating efficiency in particular with regard to its performance and energy costs being improved and its service life prolonged, wherein in particular constructing or designing the piston compressor to be optimized for one-sided wear, which is therefore both complex and expensive, is no longer necessary. In particular, one-sided stress on the seal between the piston and the cylinder housing is considerably reduced by alternating the rotation directions, since the sealing and guiding elements of the piston are subject to uniform wear and not just wear on one side.

[0021] Generally speaking, use of the concept in accordance with the present disclosure as explained above with a reversal (depending on requirements) of the rotation direction of a drive shaft is possible not only for piston compressors, but also for other mechanical piston/cylinder devices, in particular for motor vehicles and/or aircraft, and also for heat pumps etc., having at least one drive shaft operable by means of a cylinder/piston arrangement, in particular internal combustion engines, compressors and motors and other / general compressor devices for hydraulic and/or pneumatic compression of media.

[0022] It is furthermore conceivable to employ the concept in accordance with the present disclosure also for piston systems with several cylinder/piston units, for example inline engines/compressors, V-type engines/compressors, Wankel (rotary) engines/compressors, boxer engines/compressors, radial engines/compressors and similar.

[0023] The present disclosure also relates to a method for operating an internal combustion engine and/or a compressor device or compressor, wherein at least one compressor element is driven, at least indirectly, by a drive shaft rotatable about a rotary axis in at least one rotation direction, in order to compress a medium or to perform driving work, wherein the design in accordance with the present disclosure is implemented.

[0024] According to a development, it is provided that the rotation direction parameter takes into account a useful signal, in particular a number-of-starts signal, a number of revolutions and/or an operating time, wherein the useful signal characterizes a predeterminable state of use, in particular a predeterminable number of starts and/or a predeterminable number of revolutions and/or a predeterminable operating time.

[0025] This development thus relates to a (preset) regular, and (in some aspects) automatic, alternation of the rotation direction. The useful signal is taken into account for that purpose.

[0026] The useful signal characterizes the preceding use of the piston compressor. The useful signal includes in particular a preceding number of starts of the piston compressor (number-of-starts signal). The useful signal can also comprise a number of revolutions of the drive shaft, wherein the revolutions may be separated by rotation direction, wherein it is recorded how many revolutions in the counterclockwise direction and how many revolutions in the clockwise direction have already taken place beforehand. The useful signal may also comprise an operating time or duration, which may be recorded separately by rotation direction in the same way as the number of revolutions.

[0027] With regard to the useful signal, it may be provided that a regular alternation, e.g., a change in the rotation direction, is generally performed depending on the number of preceding starts, on a number of revolutions in each rotation direction and/or on an operating duration in each direction. For example, the rotation direction is changed when a defined threshold value is reached after a definable number of starts, revolutions and/or operating duration in the same direction. Alternatively, actual use can be recorded separately by rotation direction. For example, it is recorded how often the piston compressor was started in the counterclockwise direction, how many revolutions were performed in the counterclockwise direction and/or how long operation in the counterclockwise direction took place. Depending on that, the rotation direction can be changed such that the piston compressor is, starting from a defined threshold value for operation in the counterclockwise direction, operated in the clockwise direction to ensure uniform wear. Taking the useful signal into account advantageously leads to a general reduction in wear due to uniform use.

[0028] According to a development, it is provided that the rotation direction parameter takes into account an event signal, in particular a sensor signal, a user signal or an error signal. This development relates to a deliberate or selective reversal of the rotation direction. The event signal is generated and transmitted only when the corresponding event has happened, whereupon the rotation direction is changed. The event signal may be, for example, a user input (pressing of a button), the detection of uneven wear on the components of the piston compressor, or an error message (for example jamming of the drive shaft in its current rotation direction). The rotation direction is reversed in particular irregularly or whenever required. The service life, performance and/or operating efficiency of the piston compressor are advantageously further improved as a result.

[0029] According to a development, it is provided that the event signal comprises a sensor signal characterizing a mechanical variable and/or an electrical variable. The mechanical variable and/or electrical variable may be, for example, wear on the components of the piston compressor or a starting current, e.g., the current required to start up the drive motor from standstill, which is detected by a correspondingly designed sensor. Advantageously, this allows the rotation direction to be optimized to suit requirements or adjusted to the current operating conditions.

[0030] According to a development, it is provided that the sensor signal characterizes a motor current, in particular a starting current, a connecting rod position at the time of starting the drive motor, in particular a drive shaft position, and/or a wear state, wherein the rotation direction parameter is determined depending on at least one predeterminable threshold value of the sensor signal. The drive shaft position is the angle of the drive shaft during starting, using which the position of the connecting rod, via which the compressor piston is indirectly driven by the drive shaft, can be deduced. A wear state, for example an increase in leakage at a seal, in particular between two components such as the compressor piston and a housing wall of the compressor cylinder, or an increased frictional resistance in the piston movement or in a bearing ring, can be ascertained from a decrease in a compressed air generation rate, from an increase in the power input, or from other secondary variables. In this development, it is provided that whenever it is detected by the sensor that the starting current needed to start the drive motor in the preceding rotation direction, e.g. the counterclockwise direction, is higher than in the other rotation direction, e.g. the clockwise direction (in particular due to the connecting rod position/drive shaft position and/or wear), the drive shaft is now rotated in that rotation direction requiring correspondingly less current during starting. It may also be determined, based on the connecting rod position or drive shaft position, in which rotation direction the drive motor would be working against a pressure present in the piston cylinder, requiring correspondingly greater power. Based on that, the rotation direction can be selected such that during starting the drive motor works with, and not against, the compression pressure, and needs less electric power for starting. It is also possible, as already explained above, to take into account the detected previous wear (in the previous rotation direction) for determining the further rotation direction. The service life, performance and/or operating efficiency of the piston compressor are advantageously further improved as a result.

[0031] According to a development, it is provided that the sensor signal for the connecting rod position, e.g., for an angle of the drive shaft, determines the rotation direction parameter in a decompression direction of the compressor cylinder inside the compressor piston. The decompression direction is that movement direction of the compressor piston inside the compressor cylinder which leads to suction of the air and hence in contrast to a compression direction opposite the decompression direction - does not compress the sucked-in air. In other words, it is determined as already indicated in the foregoing on the basis of the connecting rod position which potential rotation direction of the drive shaft (counterclockwise or clockwise) at the time of starting corresponds to the decompression direction. It is thus determined when starting whether the drive shaft would rotate the piston in the decompression direction by rotation either in the counterclockwise direction or in the clockwise direction. Based on that determination, the rotation direction parameter or the rotation direction initiated with it can be determined or selected such that the drive shaft moves the compressor piston in the decompression direction. This has the advantage that the starting current needed for the drive motor is considerably reduced, since the compressor piston does not have to work against a compression pressure as would be present in the compression direction.

[0032] According to a development, it is provided that the sensor signal of the motor current determines the rotation direction parameter with regard to a minimized starting current. Hence the rotation direction is, as already explained, selected on the basis of the sensor signal such that the starting current needed for starting the drive motor is as minimal as possible. Advantageously, the piston compressor is particularly energy-efficient to operate as a result.

[0033] According to a development, it is provided that the sensor signal of the wear state, e.g., of an abrasion or friction state, of an operating pressure state, or of the operating current behavior, determines the rotation direction parameter with regard to a minimized wear state. A wear sensor may be for example a sensor for operating current, for compressed air or for friction. The rotation direction is selected by the appropriately determined rotation direction parameter such that the drive shaft does not rotate in that rotation direction in which increased wear is already ascertainable. For example, the actual wear is characterized based on the abrasion or friction state, on the operating pressure state or on the operating current behavior in one rotation direction, for example counterclockwise rotation, and it is thus detected that the compressor power in this rotation direction is already decreasing due to wear. In the other rotation direction however, for example clockwise rotation in this case, the wear is reduced such that a compressor power is achievable which is higher than in the other rotation direction.

[0034] Accordingly, the rotation direction is then selected for optimized performance, such that the performance of the piston compressor is advantageously maintained or prolonged.

[0035] The present disclosure further relates to a piston compressor for a motor vehicle, in particular to an air spring compressor of an air suspension system or compressed-air sensor cleaning system of the motor vehicle, with at least one compressor piston movable inside a compressor cylinder, which is drivable at least indirectly by a drive shaft of a drive motor rotatable about a rotary axis in at least one rotation direction, in order to compress sucked-in air, and with at least one control device that controls and operates the drive motor.

[0036] In accordance with the present disclosure, it is provided that the control device is configured to perform the method in accordance with the present disclosure, as described above. To do so, the drive motor is configured as a rotation direction-reversible motor, for example as a DC or AC or three-phase motor. In particular, the motor is configured as a DC motor with permanent magnets, with a rotation direction setting on the basis of a DC polarity, or as a multiphase rotating-field-controlled AC motor with adjustable speed based on a rotating field direction setting. This results in the advantages already stated above in this respect.

[0037] According to a development, a useful signal generating unit and/or event signal generating unit comprised in the control device is/are provided and configured to supply the rotation direction parameter for generating a rotation direction actuating current of the drive motor. The rotation direction actuating current determines or leads to rotation of the drive shaft in the intended rotation direction. The actuating current can influence a rotation direction of the motor as a DC or AC motor by a current polarity or by a rotating field setting, for example by means of PWM signals. The rotation is initiated by the rotation direction actuating current. This results in the advantages already stated above.

[0038] The term comprise describes in the present case only a general (functional) association, in this case of the useful signal generating unit and/or event signal generating unit with the control device, and in that sense not limited to an actual structural integration of the useful signal generating unit and/or event signal generating unit into the control device. Stated simply, it is sufficient for the useful signal generating unit and/or event signal generating unit to be in a functional relation in some way to the control device, or for these to be associated with one another, e.g. to communicate by signals, without necessarily having to be structurally connected.

[0039] A structural integration may however also of course be provided.

[0040] According to a development, it is provided that a number-of-starts recording means, a number-of-revolutions recording means and/or an operating time recording means is/are provided in the useful signal generating unit. This results in the advantages already stated above in this respect.

[0041] According to a development, it is provided that a sensor signal processing means comprised in the event signal generating unit is provided for processing a sensor signal of a starting current, of an operating current, of a connecting rod position, in particular a drive shaft position, and/or of a wear state. This results in the advantages already stated above in this respect.

[0042] FIG. 1 shows in a simplified cross-sectional view an embodiment of a piston compressor 10 in accordance with the present disclosure.

[0043] The piston compressor 10 is designed to generate compressed air and to feed it into a downstream system. In the present case, the piston compressor 10 is designed as a single-stage or two-stage air spring piston compressor for a motor vehicle air suspension system, not illustrated in detail here for reasons of clarity. Air spring bags in particular of the air suspension system are thus fillable with compressed air by means of the present piston compressor 10, wherein the air suspension system represents the aforesaid downstream system. The piston compressor 10 can however be used alternatively or additionally in a compressed-air sensor cleaning system, not indicated in detail.

[0044] The piston compressor 10 has a compressor cylinder 12 or a housing in which a compressor piston 14 is mounted vertically movable in a lifting movement, as shown in FIG. 1 by an arrow 16. The piston compressor 10 furthermore has a drive motor 18, with settable rotation direction, arranged on the outside of the compressor cylinder 12 and designed for generating a driving force for the lifting movement of the compressor piston 14.

[0045] For transmitting the driving force and converting it to the lifting movement, the drive motor 18 is operatively connected to the compressor piston 14 via a rotatably mounted drive shaft 20 and a connecting rod 22. The drive shaft 20 has a rotary axis 24 about which the drive shaft 20 is rotatable in a rotation direction 26, as shown in FIG. 1 by a round arrow.

[0046] The compressor piston 14 is thus indirectly coupled to the drive motor 18 via the drive shaft 20 and the connecting rod 22, in order to convert the driving force generated in the drive motor 18 to a lifting movement of the compressor piston 14. The driving force generated by the drive motor 18 is transmitted to the drive shaft 20, whereby the latter is set in rotation about the rotary axis 24 in the rotation direction 26. The connecting rod 22 is in turn mechanically coupled to the drive shaft 20 or in the present case part of the drive shaft 20, and is designed to transmit the rotational movement of the drive shaft 20 generated by the drive motor 18 into the lifting movement of the compressor piston 14.

[0047] The piston compressor 10 furthermore has an inlet 28, provided in the compressor cylinder 12 or housing, through which air from the surrounding atmosphere is suckable into the interior of the compressor cylinder 12. Furthermore, the piston compressor 10 has an outlet 30 provided in the compressor cylinder 12, by means of which the compressed air generated by the piston compressor 10 is transferrable into the downstream system. The inlet 28 and the outlet 30 are fluidically coupled to a piston chamber 32, provided in the compressor cylinder 12, inside which the compressor piston 14 is movably mounted. In some aspects, (controllable) valves, in particular non-return valves, not shown in the present case for reasons of clarity, are arranged between the inlet 28, the outlet 30 and the piston chamber 32 to prevent uncontrolled inflow and outflow of the air, in particular backflow.

[0048] To generate the compressed air, the compressor piston 14 is set to a downward movement by means of the drive motor 18, the drive shaft 20 and the connecting rod 22. This generates a negative pressure in the piston chamber 32, as a result of which air is sucked from the surrounding atmosphere into the piston chamber 32 via the inlet 28. The previously sucked-in air located inside the piston chamber 32 is compressed and forced via the outlet 30 into the downstream system by a subsequent upward movement of the compressor piston 14. This procedure is repeated until sufficient compressed air has been generated and fed into the downstream system.

[0049] Generic piston compressors, previously known from the prior art and hence with a similar structure and operation are usually designed such that the corresponding drive shaft is always rotatable only in one and the same rotation direction, and the rotation direction of the respective drive shaft is thus fixed and not changeable. Accordingly, the known piston compressors usually display one-sided wear, which in known solutions is compensated for at least partially by a corresponding structural design or specification of the piston compressor.

[0050] By contrast, the present piston compressor 10 as explained above is however advantageously designed such that the rotation direction 26 of the drive shaft 20 is controllable or may be deliberately changed, in the present case reversed, depending on definable parameters.

[0051] For that purpose, the present piston compressor 10 has a control device 34, as shown by way of example in FIG. 1 and coupled by means of signals to the drive motor 18, which is designed to generate at least one definable rotation direction parameter 36. Depending on the rotation direction parameter 36, the rotation direction 26 of the drive shaft 20 is deliberately reversed when the drive motor 18 is started.

[0052] The rotation direction parameter 36 may comprise various types of signals determining the rotation direction 26 to be effected. In the present case, these signals are in particular a useful signal and/or an event signal. The control device 34 has an event signal generating unit 38 and a useful signal generating unit 40 which can generate the respective signal and incorporate it into the rotation direction parameter 36. The event signal generating unit 38 and the useful signal generating unit 40 furthermore have recording and/or processing means (e.g., a recording unit configured to record at least one of a number of starts, a number of revolutions, or an operating time and/or a processor configured to process a sensor signal of one or more of a starting current, an operating current, a drive shaft position, or a wear state), not shown in the present case for reasons of clarity, for determining and generating the event signal or useful signal.

[0053] Accordingly, the present piston compressor 10 explained on the basis of FIG. 1 is advantageously operable in accordance with an advantageous method explained in the following, in which method the rotation direction 26 of the drive shaft 20 is advantageously changeable or influenceable by the rotation direction parameter 36 when the drive motor 18 is started.

[0054] FIG. 2 shows in this connection a flow diagram in which the sequence of the method is shown by way of example.

[0055] The method starts with a first step S1, in which the drive motor 18 for generating compressed air is to be started.

[0056] In a subsequent second step S2, the rotation direction parameter 36 is determined, based on which the rotation direction 26 of the drive shaft 20 is fixed, as already explained above, for subsequent operation of the drive motor 18 or piston compressor 10.

[0057] To determine the rotation direction parameter 36 as part of step S2, the useful signal is determined or generated in a first partial step S2A. Additionally or alternatively, the event signal can be determined or generated in a second partial step S2B. The rotation direction parameter 36 is then determined in step S2 depending on the useful signal and/or generation signal.

[0058] The useful signal comprises or characterizes the preceding use of the piston compressor 10. In this connection, the useful signal can for example comprise a number-of-starts signal which characterizes the number of preceding starts of the drive motor 18. The useful signal can also comprise a number of previous revolutions of the drive shaft 20 and/or an operating time or duration of the piston compressor 10. The useful signal generating unit 40 of the control device 34 has the appropriate and already mentioned recording means for recording the number of starts, revolutions and/or previous operating time.

[0059] Depending on the preceding starts, revolutions and/or operating time recorded and on the information associated therewith on how long and how often the drive shaft 20 has already been rotated in the one rotation direction 26 beforehand, the useful signal is generated as part of partial step S2A. The useful signal defines here whether it is now necessary for the now intended start of the drive motor 18 to reverse or maintain the previous rotation direction 26 based on previous use.

[0060] If the result of determining the useful signal in step S2A is that the drive shaft 20 has now been rotated long enough in the previous rotation direction 26, the useful signal is now generated such that the rotation direction parameter 36 containing the useful signal now reverses the rotation direction 26 at the intended start of the drive motor 18. If however the useful signal shows that the drive shaft 20 can continue to rotate as before in the same rotation direction 26, the useful signal is generated such that the drive shaft 20 continues to rotate in the same rotation direction 26 at the now intended start of the drive motor 18 based on the rotation direction parameter 36.

[0061] Additionally or alternatively, the event signal can be determined and generated in step S2, partial step S2B, when determining the rotation direction parameter 36. The event signal relates here to a deliberate reversal of the rotation direction 26 depending on an event. This event may be for example a user input or a user signal or an error signal.

[0062] In particular, the event signal however comprises a sensor signal which characterizes a mechanical variable and/or an electrical variable. This mechanical variable and/or electrical variable is, for example, a wear state of the piston compressor 10. In some aspects, the electrical variable may be a starting current of the drive motor 18 and/or a position of the connecting rod 22 at the time of starting.

[0063] The underlying idea is that the rotation direction parameter 36 is determined, using the sensor signal or event signal, such that the drive motor 18 needs a minimized starting current for an intended start. To do so, in particular the position of the connecting rod 22 at the time of starting is determined. The position of the connecting rod 22 is determined using the angle of the drive shaft 20 at the time of starting, by which the position of the connecting rod 22 can be deduced with simple and known mathematical methods.

[0064] To minimize the starting current, the rotation direction 26 is selected such that the connecting rod 22 is moved in a decompression direction of the compressor piston 14 when the drive motor 18 is started. As a result, the compressor piston 14 does not have to be moved against a pressure inside the compressor cylinder 12, so that less effort or energy is needed for the initial movement of the compressor piston 14, which in turn entails a minimized starting current for the drive motor 18 moving the compressor piston 14.

[0065] The event signal generating unit 38 of the control device 34 has corresponding sensor signal processing means for determining or recording the previously mentioned factors necessary for the event signal, in particular the sensor signal, in partial step S2B. Hence the event signal or the rotation direction parameter 36 in step S2 is determined in particular such that the rotation direction 26 is selected such that the drive motor 18 needs a minimum starting current, with the drive shaft 20 being moved in that rotation direction 26 which effects a shift of the compressor piston 14 in the decompression direction.

[0066] Depending on the preceding determination of the rotation direction parameter 36 in step S2 or on the determination and generation of the useful signal influencing the rotation direction parameter 36 (partial step S2A) and/or of the event signal (partial step S2B), the rotation direction parameter 36 is correspondingly generated in a subsequent third step S3 following step S2 and transmitted to the drive motor 18. As already explained in detail, the rotation direction parameter 36 generated and transmitted in step S3 comprises the control command for the rotation direction 26 of the drive shaft 20.

[0067] The drive motor 18 is thus started with the rotation direction 26, based on the rotation direction parameter 36 defined with the rotation direction parameter 36, in a subsequent fourth step S4, and operated until the end of its use for the intended purpose. At the end of its use for the intended purpose, the drive motor 18 is switched off.

[0068] The method then resumes with step 1 as soon as further operation, and hence a restart of the drive motor 18, is required. A restart can take place when the vehicle is started, or when the pressure of the air pressure system or of the main gallery of the air spring system or of the compressed-air sensor cleaning system drops below a lower limit.