WO2018184849A1

WO2018184849A1 - Method for monitoring a clutch-controlled air compressor of a vehicle

Info

Publication number: WO2018184849A1
Application number: PCT/EP2018/057185
Authority: WO
Inventors: Steffen Krebs; Christoph Wilken
Original assignee: Wabco Gmbh
Priority date: 2017-04-04
Filing date: 2018-03-21
Publication date: 2018-10-11
Also published as: DE102017003247A1

Abstract

The invention relates to a method for monitoring a clutch-controlled air compressor (1) of a vehicle. In a transfer phase of the air compressor (1), at least the following steps are carried out: (a) detecting the current motor rotational speed (n_motor) of the drive motor (3) and determining the clutch input rotational speed (n_clutch input) from the detected motor rotational speed (n_motor) and optionally a fixed ratio (i) of a transmission (5) between the drive shaft (6) and the clutch input side (4), (b) ascertaining the current compressor rotational speed (n_compressor) by means of a pressure curve analysis of the air pressure generated by the air compressor (1), (c) determining the clutch output rotational speed (n_clutch output) from the ascertained compressor rotational speed (n_compressor) and optionally a fixed ratio between the clutch output side (7) and the compressor input shaft (8), (d) comparing the clutch input rotational speed (n_clutch input) with the clutch output rotational speed (n_clutch output) by forming the rotational speed difference (n_slip) in accordance with n_slip = n_clutch input – n_clutch output, (e) specifying a slip threshold n_slip_lim > 0 for the compressor clutch (2), (f) detecting a clutch slip of the compressor clutch (2) if the ascertained rotational speed difference (n_slip) is greater than the slip threshold (n_slip_lim) [n_slip > = n_slip_lim], and (g) generating and outputting a warning signal and/or a service display in the event of a detected clutch slip.

Description

Method for monitoring a clutch-controlled air compressor of a vehicle

The invention relates to a method for monitoring a clutch-controlled air compressor of a vehicle, wherein the air compressor is driven in delivery phases for generating compressed air for an electronic air treatment unit of the vehicle by a drive motor and is decoupled from the drive motor outside the delivery phases by a controllable compressor clutch, wherein the compressor clutch Friction clutch is formed and disposed between the drive motor and the air compressor, and wherein a clutch input side of the compressor clutch with a drive shaft of the drive motor and a clutch output side of the compressor clutch is directly or indirectly connected to a compressor input shaft of the air compressor. Moreover, the invention relates to a vehicle with an air compressor, with which such a method is feasible.

Electronic air treatment units are used in motor vehicles, mainly in commercial vehicles, for supplying compressed air to pneumatic systems. Such air treatment units are usually divided into different air circuits and serve, for example, the operation of brake systems and various auxiliary consumers, such as a clutch or a transmission, or an air spring system. For the production of compressed air, an air compressor is used which, controlled by the air treatment unit, compresses air drawn in from the atmosphere. The air conditioning unit switches between pumping phases in which compressed air is needed and idle phases in which the compressor is switched off or de-pressurized. The conveyed compressed air is, if necessary, regulated by the air treatment unit, the various pneumatic consumers of the vehicle provides.

The air compressor can be flanged directly to an internal combustion engine of the vehicle and driven by this. For this the air compressor is over Gear transmission or a traction drive either permanently connected to the drive shaft of the engine or decoupled by a controllable compressor clutch from the drive shaft.

DE 10 2010 033 539 A1 and DE 10 201 1 100 512 A1 describe by way of example methods for controlling compressed air systems for commercial vehicles with compressors, which can be coupled to the drive motor or coupled via a coupling.

The air compressed by the air compressor is stored in a compressed air reservoir. As soon as the pressure in the reservoir reaches a maximum, the air treatment unit switches off the conveying operation. When the pressure in the compressed air reservoir reaches a minimum, the air treatment unit switches the air compressor back into the conveying mode. Then the compressor goes through a new cycle to replenish the reservoir. Between the cycles, a continuously driven air compressor runs without pressure via a valve control, whereas a clutch-controlled air compressor is disconnected from the drive and does not run with it. Clutch-controlled air compressors have the advantage that by completely decoupling the air compressor in those phases in which no air compression is required, a comparatively greater energy saving in the drive motor can be achieved.

However, the useful life of a friction clutch designed as a compressor clutch is limited by the operational wear on the clutch disc. At the end of this service life, the clutch begins to slip. This is the time when the clutch should be replaced to anticipate air compressor failure and possible consequential damage and cost of unscheduled vehicle stops. If there is a failure of the air compressor due to clutch wear, this happens suddenly and without any warning to the driver of the vehicle. If necessary, the vehicle must be towed to the nearest workshop. From DE 10 2008 005 437 A1 a method for controlling a system comprising a compressor, a control device and a compressor associated with the clutch is known, in which a monitoring routine is performed, in the context of which the clutch is opened or closed by means of a signal of the control unit can be to avoid damaging the clutch, compressor and the compressor downstream components. As part of the monitoring routine, a slip of the closed clutch can be detected by monitoring the compressor speed. In the known slip monitoring is first checked whether the clutch has been closed for a certain period of time. Thereafter, it is checked whether the current compressor speed is not equal to an expected compressor speed plus / minus a tolerance value. It is then checked whether the difference between the current compressor speed and the expected compressor speed plus / minus the tolerance value increases within a certain time interval and, if necessary, checks whether a counter is greater than a maximum permissible value for this counter. If so, an audible or visual warning signal is output on a display.

Against this background, the invention has the object to propose a method with which the reliability of a clutch-controlled air compressor is increased and which is also inexpensive to implement and easy to operate. In particular, a threatening, wear-related failure of a compressor clutch should be detected early. The process should manage without additional effort for a speed sensor of the air compressor. In particular, the method should be feasible on air compressors for air treatment units in commercial vehicles.

The solution of this problem arises from the features of the main claim, while advantageous embodiments and further developments of the invention are the dependent claims can be removed.

The invention was based on the finding that in a friction clutch-controlled air compressor, a perfect compressed air delivery operation depends on the correct function of the compressor clutch. Accordingly, the air compression in the was influenced and disturbed by a wear-related impairment of the torque transmission capability of the compressor clutch. At the end of its useful life, the clutch begins to slip. If the clutch is worn, it will spin without warning, and the compressor will not be able to run, and it will not be able to provide compressed air to the vehicle. An incipient clutch slip, however, is already apparent before a total failure of the clutch, when the compressor speed is lower than the engine speed and / or decreases the maximum transmissible torque of the compressor clutch. This can be detected without direct detection of the compressor speed based on a consideration of the pressure curve in a regular and / or modified in a test carried air compression in one of the air circuits of the air treatment unit of the vehicle and notified by warning signal to the driver.

The invention is therefore based on a method for monitoring a clutch-controlled air compressor of a vehicle, in which the air compressor is driven in phases for generating compressed air for an electronic air treatment unit of the vehicle by a drive motor and is decoupled from the drive motor outside the delivery phases by a controllable compressor clutch the compressor clutch is formed as a friction clutch and disposed between the drive motor and the air compressor, and wherein a clutch input side of the compressor clutch with a drive shaft of the drive motor and a clutch output side of the compressor clutch is directly or indirectly connected to a compressor input shaft of the air compressor.

To achieve the object, the invention provides that at least the following method steps are carried out in a delivery phase of the air compressor:

(a) detecting the current engine speed (n_motor) of the drive motor and determining the clutch input speed (n_coupling input) from the detected engine speed (n_Motor) and optionally a fixed ratio (i) of a transmission between the drive shaft and the clutch input side,

(b) determining the current compressor speed (n_compressor) by means of a pressure curve analysis of the air pressure generated by the air compressor, (c) determining the clutch output speed (n_coupling output) from the determined compressor speed (n_compressor) and possibly a fixed ratio between the clutch output side and the compressor input shaft,

(d) comparing the clutch input speed (n_coupling input) with the clutch output speed (n_coupling output) by forming the speed difference (n_slip) according to the equation n_clutch = n_coupling input - n_coupling output,

(e) specifying a slip limit n_slip_lim> 0 for the compressor clutch,

(f) detecting clutch slip of the compressor clutch when the detected speed difference (n_slip) is greater than the slip threshold (n_slip_lim)

[n_slip> = n_slip_lim], and

(G) generating and outputting a warning signal and / or a service indicator when detected clutch slip.

By the method, the operability of the friction clutch of a clutch-controlled compressor can be monitored and warned the driver of the vehicle in good time before an impending failure of the air compressor due to a wear-related slippage of the clutch. This allows the driver to avoid an unscheduled, damage-related stop of the vehicle. According to the invention, no direct measurement of the compressor speed is required for this purpose. This can be dispensed with a costly speed sensor for detecting the compressor speed. An imminent end of the service life of the clutch can therefore be derived from the pressure curve during the air compression. The values of the pressure curve are in any case available through a conventional pressure sensor system present in the air treatment unit and can be used for carrying out the method. For the method, only an adaptation of the control software in the air treatment unit and a display option, such as a red warning light in a display panel, required.

According to one embodiment of the invention, it may be provided that in the pressure profile analysis in at least one air circuit of the air treatment unit or in a pressure accumulator connected to this air circuit at a defined engine speed. speed (n_Motor) by means of a pressure sensor regularly recurring pressure peaks are measured, which are generated during the air compression of the air compressor, and that from the time interval T of two immediately successive pressure peaks (peak_1, peak_2) the current compressor speed (n_Kompressor) according to Equation n_compressor = 1 / T is determined.

Air compressors for commercial vehicles often have a piston-cylinder design. DE 10 2010 034 409 A1, for example, shows such a two-cylinder reciprocating compressor in which a compressor input shaft designed as a crankshaft is arranged in a crankcase. Above the crankcase is a cylinder block with the two cylinders, in each of which a piston is arranged. In air compression, each piston generates a pressure spike in the compressed air at each crank-shaft rotation at a given crank angle. The time interval of the successive pressure peaks is thus linked directly with the current speed of the crankshaft or with the current speed of the compressor input shaft.

Accordingly, the pressure sensor of the air treatment unit pressure peaks, which are generated during the air compression by a piston movement in a piston cylinder of a reciprocating compressor, detect by measurement. These measured values are forwarded to a control device for their evaluation. This pressure scanning can be done for example in an air circuit of the service brake of the vehicle and is preferably carried out at a defined speed of the drive motor, for example, at engine idle speed. The time difference (T) between two pressure peaks can be converted into the compressor speed (n_compressor). This compressor speed (n_Compressor) is compared with the engine speed (n_Motor), which is for example read from a data bus of the vehicle. If the compressor is driven via a transmission, for example a pair of gears, the then known transmission ratio (i) between the drive shaft of the drive motor and the clutch input side is taken into account in the speed comparison. A transmission between the clutch output side and the compressor input shaft may also be considered, if any. The control unit checks whether there is a speed difference between the compressor speed (n_compressor) and the engine speed (n_motor) caused by the clutch. In particular, it is determined whether the actual compressor speed (n_compressor) is less than the engine speed (n_Motor) or less than the derived therefrom, expected compressor speed (n_Kompressor). This speed difference is the slip of the clutch. By means of a slip limit value, it is expedient to allow a certain tolerance in the speed difference in order to avoid a misinterpretation. If, however, the predetermined slip limit value is exceeded and the slip is therefore too great, the method or the control device recognizes a near end of the torque transmission capability of the clutch due to wear of the friction surfaces and signals an imminent clutch failure. For example, this may be indicated to the driver by a red light on a slip symbol on the instrument panel of the vehicle. The vehicle can then be brought to the workshop within a certain mileage or operating hours to replace the nearly worn clutch in good time before a failure.

According to a further embodiment of the invention, it can be provided that, in a pressure curve analysis, a switch-off pressure (p_cut-off), in which the air compressor is decoupled from the drive motor in normal operation, is increased for a short time, that in a certain time interval following, the new switch-off pressure (p_cut-off) p_cut-off), and / or the pressure peaks expected in this time interval are checked, and if the expected pressure increase and / or the expected pressure peaks are absent, a compressor speed (n_compressor) of zero or approximately zero is concluded.

Thus, the shutdown pressure of the air compressor may be increased from time to time for a short time interval by the air conditioning unit. For the higher compression, a correspondingly higher torque to be transmitted compared to a normal operation is required. A nearly worn-out compressor clutch would be transmitted by attempting to transmit the higher torque for slipping. introduced. If the increased cut-off pressure is not achieved and instead no further increase in pressure occurs within a certain time interval and / or no pressure spikes can be detected by the air conditioning unit, this is interpreted as a nearly worn clutch which can not transmit the test increased torque and completely slips so that the input shaft of the air compressor can not be rotated. If the clutch slips completely, it is preferably opened to prevent overheating damage.

This check may preferably be additionally performed to confirm a clutch slip already detected by means of the speed comparison of engine speed and compressor speed. Basically, however, even by this review an impending loss of coupling is recognizable.

In addition, it can be provided that when the clutch slip is detected, a gentle operation for protecting the compressor clutch is activated, in which the cut-off pressure of the air compressor is permanently reduced as long as clutch slip is present.

Accordingly, as soon as an imminent clutch failure is detected and signaled, the total pressure in the compressed air system of the vehicle can be reduced by the air treatment unit in the protective mode. In order to protect the compressor clutch and the air compressor and to be able to delay a failure at least, the pressure in the pneumatic system can be lowered by a corresponding control of a valve device of the air treatment unit to the reduced pressure and this value can be set as a new cut-off pressure for the air compressor.

This reduces the torque load on the compressor clutch compared to normal operation. This makes it possible for the driver of the vehicle to replace the compressor clutch or the complete air compressor with the clutch in good time before a failure, ie within a certain operating time and / or within a certain distance traveled. Within the gentle mode, the clutch operation and the compressed air supply for the vehicle are switched off. secured at a minimum level. After replacing the compressor clutch, the gentle mode is ended and normal operation is reactivated.

It is advantageous if the method is carried out at least after each new switching on of the air compressor. However, it can also be carried out continuously in the respective delivery phases of the air compressor. As a result, the operational readiness of the air compressor is monitored at all times. It is also possible that the method in each case after a predetermined number of operating hours of the air compressor, after a predetermined number of driving kilometers of a vehicle equipped with the air compressor, at specified maintenance intervals and / or if necessary, on request of an operator is performed. A wear test of the compressor clutch according to the method of the invention may for example be an integral part of the service work during a maintenance stay of the vehicle in a workshop.

Finally, the invention also relates to a vehicle, for example a commercial vehicle, with a clutch-controlled air compressor, which is operable to carry out a method according to at least one of the method claims.

It should be noted that in clutch-controlled air compressors, which already have a speed sensor for direct measurement of the compressor speed, the method according to the invention can advantageously be carried out in addition to increase the reliability of the clutch wear detection yet. In particular, a more accurate wear test of the compressor clutch can be carried out with the aid of a pressure curve analysis in comparison to conventional methods. A Schonbetrieb as he can be provided according to an embodiment of the invention can be used advantageously in each case with detected clutch slip.

The invention will be explained in more detail with reference to embodiments illustrated in the accompanying drawings. In the drawing shows 1 shows a basic structure for carrying out the method according to the invention,

2 is a diagram of a pressure curve of an air compression of a reciprocating compressor for determining the compressor speed, and

3a shows a diagram for torque transmission with an intact compressor clutch, FIG. 3b shows a diagram for transmitting torque when the compressor clutch is almost worn,

Fig. 3c is a diagram for torque transmission at almost worn compressor clutch in a Schonbetrieb.

Accordingly, an air compressor 1 shown in FIG. 1 can be connected via a compressor clutch 2 designed as a friction clutch to a drive motor 3 designed as an internal combustion engine and can be separated therefrom. A clutch input side 4 of the compressor clutch 2 is connected to a drive shaft 6 of the drive motor 3 via a transmission 5 designed, for example, as a gear transmission. A clutch output side 7 of the compressor clutch 2 is connected to a compressor input shaft 8 of the air compressor 1. By closing the compressor clutch 2, the air compressor 1 can be switched to the conveying mode when the drive motor 3 is running. By opening the compressor clutch 2, the air compressor 1 can be decoupled from the drive motor 3.

The air compressor 1 is formed in the embodiment shown as a two-cylinder piston compressor. This type of construction, which is frequently used in commercial vehicles, is known, for example from DE 10 2010 034 409 A1, and therefore does not need to be explained in more detail. The air compressor 1 accordingly has a crankcase 9, in which the compressor input shaft 8 designed here as a crankshaft is rotatably mounted. The compressor input shaft 8 is connected via connecting rods with a first piston 10 which moves in a first cylinder 1 1, and with a second piston 12 which moves in a second cylinder 13. By the piston movement sucked atmospheric air is compressed in a compressor chamber 14. The compressor chamber 14 is pneumatically connected via a connecting line 15 with an electronic air treatment unit 1 6. Such an air treatment unit 1 6 is described for example in DE 10 201 1 107 490 A1 and therefore need not be explained in detail at this point. The air treatment unit 16 is connected via a control line 26 to a control unit 29, so that electropneumatic valves of the air treatment unit 1 6 are controllable by the control unit 29.

The air treatment unit 1 6 has several separate air circuits, of which in Fig. 1, only a first air circuit 17 and a second air circuit 18, for example, a service brake, and a third air circuit 19, for example a parking brake, are indicated. The first air circuit 17 has a first compressed air reservoir 20 and the second air circuit 18 has a second compressed air reservoir 21. In the third air circuit 19, a further accumulator is provided only optional and therefore shown with a dashed line. The air treatment unit 1 6 has a pressure sensor 24 with a plurality of pressure sensors, of which a first pressure sensor 22 is connected to the connecting line 15. An illustrated second pressure sensor 23 is connected to the first air circuit 17. The two pressure sensors 22, 23 are connected via sensor lines 27, 28 to the control unit 29. The control unit 29 is also connected via a further sensor line 25 with a speed sensor on the drive motor 3, which detects the speed n_Motor of the drive shaft 6 of the drive motor 3. This speed information can also be read by a CAN bus of the vehicle. In addition, a warning device designed as a warning device 30 is present, which is connected via a signal line 31 to the control unit 29. The control unit 29 and the air treatment unit 1 6 can also be structurally combined in a housing, not shown.

The designed as a piston compressor air compressor 1 of FIG. 1 compresses air in a cyclic operation, which is characterized by the movement of the piston 10, 12 in the cylinders 1 1, 13. This compression of air can be represented in a time-dependent pressure curve, which is characteristic Having pressure peaks, which arise at the time of the respective dead center of the piston movement.

2 shows therein the time pressure curve p (t) for two first cycles cyh of the first cylinder 11 and for two second cycles cyl2 of the second cylinder 13 against the crank angle KW of the compressor input shaft 8, the assignment of the Cylinder 1 1, 13 has been made arbitrary to the cycles. Accordingly, the first cycle cyh ends in each case at top dead center at a crank angle KW of 0 ° or 360 °. The second cycle cyl2 ends in each case at top dead center at a crank angle KW of 180 °. In the air compression therefore each piston 10, 12 at a certain crank angle KW generated at each full crankshaft revolution each have a pressure peak. The time interval between the pressure peaks of this pressure profile is thus directly linked to the current speed n_compressor of the compressor input shaft 8. The pressure profile can be detected continuously, for example, with the second pressure sensor 23 in the first air circuit 17 of the service brake.

For carrying out the method according to the invention, the observation of the pressure cycle in one of the two cylinders 11, 13, for example in the first cycle cyh, which is assigned to the first cylinder 11, is sufficient. At the top dead center of the associated first piston 10, a pressure peak peak_1, peak_2, etc. is generated in each case. The rotational frequency f = 1 / T of the compressor input shaft 8 results from the time interval T [s] of two pressure peaks peak_1, peak_2. From this, the compressor speed n_compressor can be calculated directly according to the equation n_compressor = f x 60 [1 / min].

The compressor speed n_compressor corresponds to the clutch output speed n_coupling output, since in the exemplary embodiment shown, the clutch output side 7 is connected directly to the compressor input shaft 8. The engine speed n_Motor is assumed to be known. As mentioned, this can be read from a data bus CAN of the vehicle (FIG. 1). Since the compressor clutch 2 only indirectly, so via the transmission 5 with the drive shaft 6 of the drive motor sector 3 is connected, the predetermined ratio i of the transmission 5 must be taken into account. The clutch input speed n_coupling input then results according to n_coupling input = n_motor x i. By comparing the currently determined clutch input rotational speed n_coupling input with the clutch output rotational speed n_coupling output, the clutch slip n_clutch results from the difference according to n_clutch = n_coupling input - n_coupling output. The speed comparison is performed during the measurement to simplify the evaluation at a defined engine speed n_Motor, for example, at the idle speed of the drive motor. 3

In the ideal case of a slip-free torque transfer of a new compressor clutch 2, the evaluation results in a slip value of n_slip = 0. In real operation, a small speed difference is usually detected. In order to tolerate this speed difference, or to avoid a misinterpretation, a slip limit n_Schlupf_lim> 0 is specified for the compressor clutch 2. A notable clutch slip of the compressor clutch 2 is then accepted and a warning signal is output if the measured slip is greater than the slip limit, ie n_slip> = n_slip_lim. Preferably, the slip limit n_Schlupf_lim> 0 is selected so that the driver is likely to have sufficient opportunity to exchange a nearly worn compressor clutch 2 in a certain period and / or after a certain distance, for example, at the latest after the next 5000 km.

In order to verify a detected clutch slip and to determine a remaining torque transmitting capability of the compressor clutch 2, a test can be performed once or from time to time in which a cut-off pressure p_cut-off of the air compressor is tentatively increased in the short term. Subsequently, to protect against a sudden failure of the air compressor 1 until replacement of a nearly worn compressor clutch 2, a gentle operation can be activated. Figures 3a, 3b and 3c show a torque transmission test of the compressor clutch 2 and a gentle operation of the air compressor 1 is a diagram in which three example cases of a calculated torque M_cal and an actual transmittable torque M_trans are faced. In the first example case according to FIG. 3a, the switch-off pressure p_cut-off has been increased from normally 12 bar to 14.5 bar. A completely intact, so wear-free compressor clutch 2 here has a torque transmission capability of M_trans = 250 Nm. The compressor clutch 2 can transmit the torque M required for the greater air compression, for example increased by about 30% to 210 Nm. The air compressor 1 or the compressor input shaft 8 is therefore rotated until reaching the new cut-off pressure p_cut-off = 14.5 bar.

The situation is different in the case of Fig. 3b with a nearly worn compressor clutch 2. The compressor clutch 2, for example, has only a torque transmission capability of M_trans = 170 Nm. This is not enough to the compressor input shaft 8 until reaching the new cut-off pressure

p_cut-off = 14.5 bar to turn. As a result, the compressor input shaft 8 completely rotates at an applied torque M of more than 170 Nm and, for example, after a short time, for example, to protect against complete destruction

20 seconds, from the air treatment unit 1 6, controlled by the control unit 29, opened. The remaining torque transfer capability of

M_trans = 170 Nm may still be enough for a relatively short period of time for the normal operation of the vehicle. However, it is certainly sufficient for a longer period of time for a Schonbetrieb shown in Fig. 3c. For this gentle operation, the switch-off pressure p_cut-off was lowered to 9 bar. The torque to be transmitted M is thereby reduced by about 20%, for example, only 140 Nm. The torque transmission is ensured until the respective reaching of the new cut-off pressure p_cut-off = 9 bar in the air compression, so that a compressed air supply of the vehicle is secured at this, now lower level. List of Reference Numerals (part of the description)

1 air compressor

2 compressor clutch

3 drive motor

4 clutch input side

5 gears

6 drive shaft

7 coupling output side

8 compressor input shaft

9 crankcase

10 First piston

1 1 First cylinder

12 second piston

13 second cylinder

14 compressor room

15 connecting line

16 air treatment unit

17 First circle of air

18 Second air circle

19 Third circle of air

20 First accumulator

21 Second pressure accumulator

22 First pressure sensor

23 Second pressure sensor

24 pressure sensor

25 sensor line for engine speed; CAN bus

26 control line

27 First sensor line for air pressure

28 Second sensor line for air pressure

29 control unit

30 Display device, warning light 31 signal line

cyM First cycle

cyl2 Second cycle

KW crank angle

i translation

M torque

M_cal Calculated torque

M_trans Transmittable torque

n engine engine speed

n_coupling input clutch input speed n_coupling output clutch output speed n_compressor compressor speed n_slip speed difference, slip n_slip_lim slip limit value

p pressure

p_cut-off switch-off pressure

peak_1 First pressure peak

peak_2 Second pressure peak

t time

T time interval

Claims

claims

1 . Method for monitoring a clutch-controlled air compressor (1) of a vehicle, in which the air compressor (1) is driven by a drive motor (3) in delivery phases for generating compressed air for an electronic air treatment unit (16) of the vehicle and by a controllable compressor clutch (2 ) is decoupled from the drive motor (3), wherein the compressor clutch (2) is formed as a friction clutch and between the drive motor (3) and the air compressor (1) is arranged, and wherein a clutch input side (4) of the compressor clutch (2) with a drive shaft (6) of the drive motor (3) and a clutch output side (7) of the compressor clutch (2) with a compressor input shaft (8) of the air compressor (1) is directly or indirectly connected, characterized in that in a delivery phase of the air compressor (1) at least following Procedural steps are carried out:

(A) detecting the current engine speed (n_Motor) of the drive motor (3) and determining the clutch input speed (n_Kupplungseingang) from the detected engine speed (n_Motor) and optionally a fixed ratio (i) of a transmission (5) between the drive shaft (6) and the Coupling input side (4),

(b) determining the current compressor speed (n_compressor) by means of a pressure curve analysis of the air pressure generated by the air compressor (1),

(c) determining the clutch output speed (n_coupling output) from the determined compressor speed (n_compressor) and optionally a fixed ratio between the clutch output side (7) and the compressor input shaft (8),

(e) specifying a slip limit value n_slip_lim> 0 for the compressor clutch (2),

(f) Detecting clutch slippage of the compressor clutch (2) if the determined speed difference (n_slip) is greater than the slip limit value (n_slip_lim)

[n_slip> = n_slip_lim], and (G) generating and outputting a warning signal and / or a service indicator when detected clutch slip.

2. The method according to claim 1, characterized in that in the pressure curve analysis in at least one air circuit (17, 18, 19) of the air treatment unit (1 6) or in an air circuit to this (17, 18, 19) connected pressure accumulator (20, 21 ) at a defined engine speed (n_Motor) by means of a pressure sensor (24) regularly recurring pressure peaks are measured, which are generated during the air compression of the air compressor (1), and that from the time interval (T) of two immediately successive pressure peaks ( peak_1, peak_2) the current compressor speed (n_compressor) according to the equation

n_compressor = 1 / T is determined.

3. The method according to claim 1 or 2, characterized in that in a pressure curve analysis, a cut-off pressure (p_cut-off), wherein the air compressor (1) is decoupled in a normal operation by the drive motor (3) is briefly increased, that in one following a certain time interval, a pressure increase corresponding to the new cut-off pressure (p_cut-off) and / or the pressure peaks expected in this time interval are checked, and in the event that the expected pressure rise fails and / or the expected pressure peaks fail to reach a compressor speed (n_compressor) of Zero or nearly zero is closed.

4. The method according to any one of claims 1 to 3, characterized in that when detected clutch slip a gentle operation to protect the compressor clutch (2) is activated, in which the cut-off pressure (p_cut-off) of the air compressor (1) is permanently reduced, as long as clutch slip is determined.

5. The method according to any one of claims 1 to 4, characterized in that the method is carried out at least after each new switching on of the air compressor (1).

6. The method according to any one of claims 1 to 5, characterized in that the method is carried out continuously in the respective delivery phases of the air compressor (1).

7. The method according to any one of claims 1 to 5, characterized in that the method in each case after a predetermined number of operating hours of the air compressor (1), after a predetermined number of kilometers of a vehicle with the air compressor (1) equipped vehicle, at fixed maintenance intervals and / or, if necessary, at the request of an operator.

8. vehicle, such as commercial vehicle, with a clutch-controlled air compressor (1), which is operable to perform a method according to at least one of the method claims.