Operating strategy for limiting the power consumption of a brushless motor for electrically driven passenger-car air-spring compressors through mode switching
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-04-24
- Publication Date
- 2026-03-18
AI Technical Summary
Brushless motor-driven car air suspension compressors face challenges in efficiently managing power consumption, particularly when operating under varying load conditions, leading to excessive current consumption and potential overheating, which can reduce performance and increase noise.
A compressed air supply system that switches between closed and open operating modes based on average motor current, allowing the compressor to maintain constant speed while reducing load by switching to open mode when maximum current is exceeded, thereby optimizing performance across all operating ranges.
This approach maximizes compressor performance by avoiding worst-case assumptions and reduces noise and vibration, ensuring efficient operation even under rare operating conditions without oversizing the motor, thus maintaining consistent performance and reducing energy consumption.
Smart Images
Figure EP2024061315_14112024_PF_FP_ABST
Abstract
Description
[0001] Operating strategy for limiting the power consumption of a brushless motor for electrically driven car air suspension compressors by mode switching
[0002] The invention relates to a compressed air supply system for a vehicle. The invention also relates to a method for operating such a compressed air supply system.
[0003] In motor vehicles, compressed air supply systems can, for example, supply compressed air to an air suspension system as a compressed air consumer and / or a pneumatic braking system as a compressed air consumer. In order to provide compressed air at a sufficiently high pressure for such compressed air consumers, compressors are required to generate compressed air. Such compressors are typically driven by electric motors that consume a motor current during operation. Compressors and compressors are used synonymously in this description and refer to units that compress air.
[0004] In addition to the compressed air consumer(s), the compressor and its drive, key components of a compressed air supply system are electrically controllable valves that can be controlled by a compressed air controller – i.e., opened or closed. In this way, compressed air can be supplied to or released from the individual compressed air consumers in a compressed air supply system in a targeted manner. Depending on which compressed air consumers need to be supplied with compressed air in a given operating situation, the compression work to be performed by the compressor can vary greatly. As explained in more detail below, the torque delivered by the drive of the compressor depends on the compressed air pressure required for the respective operating situation.If the compressor or condenser is driven by an electric motor, its current consumption depends on the torque to be delivered (i.e. the operating load of the drive) at the supply voltage typically provided by the vehicle's electrical system.
[0005] Preferably, the compressor and the associated drive, in particular the associated electric motor, are combined into a single structural unit—hereinafter referred to as the compressor module. Compressor modules are used, for example, for compressed air supply systems in motor vehicles.
[0006] Brushless DC motors (BLDC motors: Brush Less Direct Current motors) are preferably used as electric motors for driving compressors or condensers. A brushless DC motor, as a so-called internal rotor, typically has a rotor equipped with electromagnetic coils, a rotor equipped with permanent magnets, and a motor controller. The motor controller is configured as an electronic commutator in such a way that the motor controller controls the power supply to the coils of the motor (hereinafter also referred to as coils) via power switches in such a way that the coils are periodically supplied with power in turn, creating a rotating magnetic field which, via magnetic forces, causes the rotor equipped with permanent magnets to rotate synchronously.Such brushless DC motors with rotors fitted with permanent magnets are therefore also referred to as PMSM motors, where PMSM stands for permanent magnet synchronous motor. The abbreviation PMSM is typically used for sine-commutated brushless electric motors, while the abbreviation BLDC (brushless direct current) is usually used for block-commutated brushless electric motors. With block commutation, the current supply to the coils (e.g. three or n times three) is digitally switched, meaning either no current or the full current is supplied to the windings of the respective coil or coils of a phase. With sine commutation, each coil of the motor is supplied with a sine wave offset by 120°, resulting in a continuously rotating magnetic field of constant strength.For the conventional speed control of a brushless electric motor, the motor is equipped with rotor angle detection devices, which include electronic sensors such as Hall sensors for detecting the rotor position. This also allows the phase angle between the applied rotating field and the mechanical rotation of the rotor to be detected, and the phase angle of the rotating field can be adjusted accordingly. BLDC motors thus behave similarly to mechanically commutated DC motors. However, brushless DC motors are more efficient, subject to less wear, and can be better controlled in terms of speed than electric motors with a brush commutator.
[0007] In compressor modules for compressed air generation in a compressed air supply system, for example, for motor vehicles, the compressor generating the compressed air and its electric motor serving as its drive form a single structural unit. For both efficient and environmentally friendly operation, the design and operation of the electric motor—for example, the brushless DC motor—represent a particular challenge. This includes, among other things, the compressor module's ability to provide sufficient compressed air to the respective compressed air supply system at all times, in all possible operating scenarios—even the rare ones. This means that a compressor module must provide sufficient compressed air for the compressed air supply system even under unfavorable conditions, which only occur rarely (1 / presFcase operating scenario).For this purpose, the drive, preferably a brushless DC motor, must also be designed accordingly. For a given electric motor's supply voltage, a higher mechanical load—i.e., a higher mechanical output power—inevitably leads to a higher current consumption of the electric motor. However, to protect a motor vehicle's electrical system, the maximum current consumption of a DC motor must be limited.
[0008] From WO 2020 / 225024 A1 it is known to operate a BLDC motor for driving a compressor at a constant speed and to reduce this speed depending on the load conditions of operating voltage and load (torque) in order to avoid over-dimensioning of the motor.
[0009] The invention is based on the object of ensuring reliable and environmentally friendly operation of a compressor module in the simplest possible way.
[0010] To achieve this object, the invention proposes a compressed air supply system, in particular for a motor vehicle, which has at least the following components: one or more compressed air consumers,
[0011] Compressed air lines, electrically controlled valves, a compressed air control system for controlling the electrically controlled valves, a compressor or condenser with an electric motor as drive, and a pressure accumulator.
[0012] The compressed air consumer(s) are or can be pneumatically connected to the compressor(s) and / or the pressure accumulator via the compressed air lines and the electrically controllable valves in such a way that the compressed air supply system can be operated either in an open operating mode or in a closed operating mode.
[0013] In closed operating mode, compressed air is supplied from the pressure accumulator to the compressed air consumer(s), or compressed air from the compressed air consumer to the pressure accumulator, in each case with the aid of the compressor. For this purpose, the electrically controlled valves and the compressor are controlled by the compressed air control system according to the closed operating mode. In open operating mode, compressed air is supplied from the ambient air to the compressed air consumer(s) or the pressure accumulator via the compressor. For this purpose, the electrically controlled valves are controlled by the compressed air control system according to the open operating mode.
[0014] According to the invention, the compressed air control system has a current signal input for a current signal representing a motor current consumed or to be consumed by the electric motor driving the compressor. The compressed air control system is designed to control the electrically controllable valves in accordance with the open operating mode of the compressed air supply system when a current signal is applied to the current signal input that represents an average motor current whose magnitude is equal to or greater than a predetermined maximum value for the motor current. The criterion for switching the operating mode is preferably not the instantaneous value of the motor current, but rather an average motor current that represents the short-term average value of the motor current, so that switching the operating mode is not triggered by a short-term current peak or cyclical fluctuations in the instantaneous value of the motor current.The value for the average motor current can, for example, be calculated by the motor control system by measuring the three phase currents and then calculating the average current consumption of the electric motor.
[0015] The invention allows the electric motor to be designed for a constant speed as standard. According to the invention, if the permissible current consumption is exceeded, the required drive power of the compressor or condenser is reduced by switching from the closed to the open operating mode. For this purpose, the current, time-averaged or low-pass filtered current consumption of the electric motor for driving the compressor or condenser is determined. If the defined limit is exceeded, the closed operation of the compressed air supply system is terminated and control is completed in the open operating mode. Mode switching based on the average motor current has the advantage that the unit-specific tolerances, the different pressure ranges, and other values influencing the current do not have to be maintained in the form of worst-case assumptions, but rather the performance of the compressor is maximized in all operating ranges.
[0016] In addition, the invention allows the speed of the compressor and drive to be kept constant, since when the maximum permissible motor current Imax is exceeded, there is no reduction in speed but a reduction in the load by switching the mode.
[0017] Advantageous further developments of the invention can be found in the dependent claims and specify in detail advantageous possibilities for realizing the concept explained above within the scope of the task and with regard to further advantages.
[0018] Preferably, the current signal input is connected to at least one current sensor, which is designed to detect a motor current IB ZU drawn from the electric motor driving the compressor and output a signal representing this current to the compressed air control system. The current sensors of the motor control system, which are usually provided for each phase, can serve as current sensors. The formation of an average motor current can already be performed by a motor control system on the compressor module or by the compressed air control system. For example, the motor control system can determine the average motor current from the three measured phase currents. Alternatively, an additional current sensor could also be provided.
[0019] In a preferred embodiment, the compressed air collector is an air suspension system of a vehicle which has one or more bellows.
[0020] Preferably, the compressor or compressor are combined with the electric motor in the form of a compressor module to form a structural unit and are thus optimally coordinated with each other on the one hand and easy to integrate as a unit into a compressed air supply system on the other.
[0021] The electric motor is preferably a speed-controlled BLDC motor, which is given at least one target speed during operation.
[0022] Particularly with regard to releasing air from the compressed air collector, for example when lowering a vehicle with an air suspension system, it is advantageous if the compressed air control is designed to predictively determine an average motor current to be absorbed by the electric motor based on an air pressure in the compressed air supply system and a request - in particular a "lowering" request - to the compressed air collector. If the predictively determined average motor current reaches or exceeds the defined maximum value for the motor current at the specified speed, the motor speed is set in a first step in such a way that the permissible current is prevented from being reached or exceeded. Advantageous here, particularly from an acoustic point of view, is the fact that the entire lowering process can thus be carried out without further speed adjustment.If the setting of this speed in the first step results in a value that is too low, the lowering process is started in open mode as a second step. It is advantageous here to avoid switching from closed to open mode during the current lowering process, as this switching requires the activation of several valves. The associated noticeable delay in the lowering process is reliably avoided with this procedure.
[0023] In the event of a "lift" request—i.e., when compressed air must be supplied to the compressed air consumer—switching from the closed to the open operating mode can be achieved simply by closing (deactivating) a boost valve. Preferably, the compressed air supply system has a pressure sensor arranged and configured to detect the air pressure prevailing in the compressed air supply system during operation and output a pressure signal representing this pressure to the compressed air control system. Based on the pressure signal and a request signal, the compressed air control system can predictively determine the required motor current and compare it with the specified maximum motor current Imax in order to effect a speed adjustment or mode change if necessary.
[0024] Preferably, the compressed air supply system comprises a reservoir valve which is pneumatically arranged between the pressure accumulator and a pneumatic main pressure line.
[0025] It is also advantageous if the compressed air supply system has a boost valve that is pneumatically arranged between the pressure accumulator and a boost and return line.
[0026] A further aspect relates to a method of claim 10. The method serves for operating a compressed air supply system, in particular for a motor vehicle, with: one or more compressed air consumers, compressed air lines, electrically controllable valves, a compressed air control for controlling the electrically controllable valves, a compressor or condenser with an electric motor as drive, and a pressure accumulator.
[0027] The compressed air consumer(s) are or can be pneumatically connected to the compressor(s) and / or the pressure accumulator via the compressed air lines and the electrically controllable valves in such a way that the compressed air supply system can be operated either in an open operating mode or in a closed operating mode.
[0028] According to the method, a current signal is supplied to the compressed air control system during operation, representing a motor current consumed or to be consumed by the electric motor driving the compressor. The compressed air control system switches the compressed air supply system from the closed to the open operating mode and controls the electrically controllable valves according to the open operating mode of the compressed air supply system when a current signal is applied to the current signal input that represents an average motor current IB whose magnitude is equal to or greater than a predetermined maximum value Imax for the motor current. The average motor current is a motor current value averaged and / or low-pass filtered over a period of a few tenths of a second.By forming a short-term average value of the motor current IB or by low-pass filtering the motor current, short-term peak values of the motor current are prevented from leading to a mode switch.
[0029] Preferably, switching from closed operating mode to open operating mode occurs when compressed air is supplied to the pressure sensor by deactivating the boost valve. For this purpose, the compressed air supply system has a boost valve that is pneumatically connected to the pressure accumulator.
[0030] According to a first advantageous variant, switching from the closed operating mode to the open operating mode occurs when compressed air is to be discharged from the pressure sensor by shutting off the compressor, closing (deactivating) the non-return valve and the reservoir valve, and opening (activating) the drain valve. For this purpose, the compressed air supply system comprises a drain valve, a non-return valve, and a reservoir valve that is pneumatically connected to the pressure accumulator.Since the average motor current is proportional to the drive torque required by the compressor (torque requirement), the selection of the open or closed operating mode can be made by predictive control without considering the motor current itself, but solely based on the influencing variables that influence the compressor's torque requirement at a given speed and their foreseeable temporal development - for example, the counterpressure that increases as the pressure accumulator fills. This - the predictive selection of the open or closed operating mode and the corresponding control of the compressed air supply system - represents an independent inventive concept that can be implemented both in combination with the mode switching based on the motor current described here and independently of the motor current.The process variants outlined below can therefore also be implemented independently of the process outlined above.
[0031] According to a first advantageous variant, if compressed air is to be discharged from the pressure sensor, the compressed air control activates the closed operating mode if the pressure in the pressure accumulator is lower than a predefined or learned accumulator pressure limit, or the open operating mode if the pressure in the pressure accumulator is higher than a predefined or learned accumulator pressure limit. For this purpose, the compressed air supply system has a pressure sensor on the compressed air accumulator, as well as a drain valve, a backflow valve, and a reservoir valve pneumatically connected to the pressure accumulator.
[0032] According to a first advantageous variant, the compressed air control activates the open operating mode in the event that compressed air is to be discharged from the pressure sensor. The compressed air control calculates or estimates the expected accumulator pressure in advance based on the available information about the accumulator pressure and the volume of the accumulator, the pressure in the compressed air sensor or one or more of its components and their volumes and heights. The control activates the open operating mode if the calculated or estimated accumulator pressure exceeds a predetermined accumulator pressure limit. The compressor then remains shut down, the reflux valve and the reservoir valve remain closed (deactivated), and the discharge valve is opened (activated).Thus, the compressor is not switched on, the return valve and the reservoir valve remain in the closed position and only the drain valve and the respective pressure pickup valves are opened.
[0033] Preferably, the compressed air control adaptively sets the storage pressure limit from a correlation of back pressure and current consumption learned during operation of the compressor module.
[0034] Embodiments of the invention are now described below with reference to the drawing. These are not necessarily intended to represent the embodiments to scale; rather, where useful for explanation, the drawing is schematic and / or slightly distorted. With regard to additions to the teachings immediately apparent from the drawing, reference is made to the relevant prior art. It should be noted that numerous modifications and changes to the form and detail of an embodiment can be made without deviating from the general idea of the invention. The features of the invention disclosed in the description, in the drawing and in the claims can be essential for the further development of the invention, both individually and in any combination.Furthermore, all combinations of at least two of the features disclosed in the description, the drawings and / or the claims fall within the scope of the invention. The general idea of the invention is not limited to the exact form or detail of the preferred embodiment shown and described below, or limited to an object that would be limited in comparison to the object claimed in the claims. For specified dimensioning ranges, values lying within the stated limits are also intended to be disclosed as limit values and to be used and claimed as desired. Further advantages, features and details of the invention will become apparent from the following description of the preferred embodiments and from the drawings, which show:
[0035] Fig. 1 is a circuit diagram of an example of a compressed air supply system including compressed air receiver in the form of air springs of a vehicle;
[0036] Fig. 2 Symbols for the valves shown in Fig. 1 to explain their operation;
[0037] Fig. 3 a compressor module with compressor, electric motor and motor control;
[0038] Fig. 4 is a sketch illustrating the operation of a brushless electric motor;
[0039] Fig. 5 Diagrams illustrating the increase in current consumption of an electric motor with increasing back pressure
[0040] Fig. 6 is a symbolic representation of a compressor and a brushless electric motor driving it with motor control; and
[0041] Fig. 7 Diagrams illustrating the effect of switching according to the invention from the closed operating mode (Fig. 7a) to the closed operating mode (Fig. 7b) on the current consumption of the electric motor driving the compressor.
[0042] The compressed air supply system 30 shown in Fig. 1 serves, for example, to supply compressed air to an air suspension system 32 having multiple air springs 34 of a vehicle. Instead of an air suspension system 32, other compressed air consumers, e.g., an air brake system, can also be pneumatically connected to the compressed air supply system 30. The term "compressed air consumer" is used herein both for an entire air suspension system 32 or air brake system, as well as for individual bellows 34 of an air suspension system 32 or air brakes of an air brake system, thus for any type of compressed air consumer.
[0043] Essential components of the compressed air supply system 30 are a compressor 12 and its drive 14, compressed air lines 22, and electrically controllable valves 44, 46, 48, 50, 52, and 54, which can be controlled—for example, opened or closed—by a compressed air control 56. In this way, compressed air can be specifically supplied to the individual compressed air consumers 34 or compressed air can be released. Depending on which of the compressed air consumers 34 needs to be supplied with compressed air in a given operating situation, the compression work to be performed by the compressor 12 can vary greatly. The compressed air control 56 is an electronic controller that can output electrical signals for activation to the individual electrically controllable valves and thus control the compressed air supply system 30. The compressed air control 56 is connected to or contains a memory 90 for operating specifications.In addition, the compressed air control 56 has various signal inputs, e.g. a signal input 90 for a request signal SAnf, a signal input 92 for a signal SIB representing a motor current IB, a signal input 94 for a signal SpAni representing an air pressure PA prevailing in a main pressure line 42 of the compressed air supply system 30, a signal input 96 for a signal SPR representing an air pressure PA prevailing in a pressure accumulator 36 of the compressed air supply system 30 and a signal input 98 for a signal SpAbn representing an air pressure PAbn prevailing at a pressure sensor 34. Instead of the compressor 12, a type of compressor can also be provided.
[0044] To increase efficiency and ensure consistent availability, so-called "closed air spring systems" are used in car air spring systems. These are air spring systems that can be operated, for example, with a compressed air supply system 30, as shown in Figure 1, because the compressed air supply system 30 has components such as a pressure accumulator 36, which enables both an open operating mode and a closed operating mode. In contrast to "open systems" or an open operating mode, in the closed operating mode the air mass in the air springs is not reduced by venting the excess air into the environment; rather, this air is pumped into the pressure accumulator 36 using the compressor 12. The compressor 12 required for this is preferably designed for two-stage compression and driven by a BLDC motor 14.The closed operating mode by pumping occurs via the second stage 12.2, in the open operating mode the compressor 12 operates in two stages by pre-compression by means of the first stage 12.1 and final compression by means of the second stage 12.2.
[0045] In order to enable a closed operating mode, the compressed air supply system 30 in the illustrated embodiment has, in addition to the pressure accumulator 36, also a return valve 48, a reservoir valve 52, a separation valve 44 and a boost valve 54.
[0046] The return flow valve 48 is pneumatically arranged between the pressure consumer 32 and the compressor 12 such that, when the return flow valve 48 is activated - i.e., open - compressed air can flow from the compressed air consumer 32 into a boost and return flow line 76 leading to the compressor 12.
[0047] The reservoir valve 52 is pneumatically arranged between the pressure accumulator and a pneumatic main pressure line 40 such that when the reservoir valve 52 is activated - i.e. open - compressed air can flow from the pressure accumulator 36 into the pneumatic main pressure line 40.
[0048] The boost valve 54 is pneumatically arranged between the pressure accumulator 36 and a boost and return line 76 such that, when the boost valve 54 is activated—i.e., open—compressed air can flow from the pressure accumulator 36 into the boost and return line 76, which leads to the compressor 12. This allows the compressor 12 to recompress the compressed air extracted from the pressure accumulator 36 during closed operation before it is supplied to the compressed air consumer 32.
[0049] The separation valve 44 is pneumatically arranged between the main pressure line 40 and the air suspension system 32 in such a way that, when the separation valve 32 is activated - i.e., open - compressed air can flow from the main pressure line 40 into the air suspension system 32.
[0050] Due to the required compressor power or the delivery capacity derived therefrom, the torques required to drive the compressor 12 in the closed operating mode differ significantly from the torque required for the open operating mode.
[0051] As already indicated, the compressed air supply system 30 shown in Fig. 1 can be operated in an open operating mode or in a closed operating mode. In the open operating mode, outside air is drawn in from the environment and compressed (see the dashed arrow in Fig. 1), and in the closed operating mode, air is drawn from a pressure vessel 36—also referred to here as a reservoir—and compressed (see the dotted arrow in Fig. 1).
[0052] While the current consumption of the compressor drive—that is, the current consumption of electric motor 14—(which is proportional to the required torque) is below approximately 25A in open mode, it can rise to 50A and more in closed mode. The closed mode is therefore the mode with the highest torque and current requirements. Both modes must be available in a vehicle.
[0053] The following describes how compressed air can be supplied to the compressed air pickups 34, for example, the spring bellows 24 of a vehicle's air suspension system 32. This is necessary, for example, if the vehicle is to be lifted on one side or all sides. For this lifting, compressed air must be supplied to the bellows 34. Open operating mode
[0054] Both raising and lowering of an air suspension system can take place in closed operating mode.
[0055] In the first open operating mode, e.g., for raising the air suspension system 12, compressed air is supplied from the compressor 12 via a pneumatic main pressure line 40 to the compressed air receiver 32—that is, the air suspension system 32—to supply compressed air to the compressed air receiver 32. Within the air suspension system 32, the compressed air is distributed by means of individual pressure receiver valves 46—which, in the illustrated embodiment, are bellows valves 46 of spring bellows 34 of the air suspension system 32.
[0056] In the illustrated embodiment, the compressor 12 is designed as a two-stage unit, comprising a first stage 12.1 and a second stage 12.2. In open operating mode, the outside air is thus pre-compressed in two stages, first by the first compressor stage 12.1 and then post-compressed by the second compressor stage 12.2.
[0057] The compressed air provided by the compressor 12 in the open operating mode can also be fed to a pressure accumulator 36 instead of to a compressed air consumer in order to create the prerequisite for a closed operating mode.
[0058] For the compressed air supply in the open operating mode, a compressor such as compressor 12 and a pneumatic main pressure line 40 are required, which supplies the compressed air provided by compressor 12 to the compressed air receiver 32. Additional components such as an air dryer 38 or a separating or isolating valve 44 are optional.
[0059] In the second open operating mode, e.g., when lowering the air suspension system 12, the drain valve is opened. This opening of the drain valve 50 causes the pneumatically controlled 3 / 2-way valve 70 to move into the working position, where venting occurs. After the drain valve 50 opens, the pressure of the air to be vented acts as a control pressure, which acts on a control piston 74 of the pneumatically controlled 3 / 2-way valve 70 and moves the 3 / 2-way valve 70 into the working position against the force of its return spring 72. Throttle valves 80.1 and 80.2 as well as two check or one-way valves 42.1 and 42.2 effectively limit the control pressure for actuating the pneumatically controlled 3 / 2-way valve 70. Closed operating mode
[0060] Both raising and lowering of an air spring system can occur in closed operating mode. In general, this means that a compressed air receiver can be supplied with compressed air in a first closed operating mode and can release air in a second closed operating mode – also known as reflow mode.
[0061] For the closed operating mode, a pressure accumulator 36, e.g., designed as a compressed air tank, a reservoir valve 52, an optional boost valve 54, a likewise optional separation valve 44, and a likewise optional return valve 48, as well as corresponding compressed air lines, are also provided. The components not required for the open operating mode—namely, the pressure accumulator 36, the reservoir valve 52, the optional boost valve 54, and the return valve 48—are shown in Fig. 1 within the dashed border 82.
[0062] In the first closed operating mode, for example, for lifting an air suspension system, air is pumped from the pressure accumulator 36 to the air suspension system 32 and into its bellows 34 by means of the compressor 12 and its second compressor stage 12.2. For this purpose, the compressor 12, the boost valve 54, and the separation valve 44 are activated, and the bellows valves 46 are opened. In this way, a vehicle can be lifted by means of the air suspension system 32 in the closed operating mode of the compressed air supply system 30 ("boost"). Since the air in the pressure vessel 36 already has a higher static pressure than the ambient outside air, the air in the closed operating mode is only recompressed by means of the second stage 12.2 of the compressor 12, and the first stage 12.1 of the compressor 12 is pneumatically ineffective in this case.
[0063] Just as in the open operating mode, in the closed operating mode the compressed air is fed via the air dryer 38 to the pneumatic main pressure line 40 and through the one-way or check valve 42.2 and is thus made available for delivery to a compressed air consumer 32.
[0064] In the second closed operating mode, for example, when lowering an air suspension system, air is pumped from the bellows 34 into the pressure accumulator 36. In this case, the compressor 12 is activated, and both the check valve 48 and the reservoir valve 52 are open, i.e., activated. Air is then pumped from the bellows 36 through the check valve 48 by means of the second stage 12.2 of the compressor 12, and through the reservoir valve 52 into the pressure accumulator 36.
[0065] Distribution of compressed air within the compressed air receiver
[0066] The compressed air is delivered to the compressed air consumer(s) 32 or the pressure accumulator 36 and distributed within the compressed air consumer 32—in the example, between the air springs 34 of the air suspension system 32—by means of electrically controlled 2 / 2-way valves 46, one of which is also shown in Fig. 2a as 2 / 2-way valve 60. In their first (rest) position, which is effected by a return spring 62, the 2 / 2-way valves 46 act as one-way or check valves. In the controlled second (activated or working) position, the 2 / 2-way valves 46 are open. The electrically controlled 2 / 2-way valves 46 are connected to an electronic compressed air control unit 56, which can be identical to an electronic control unit for controlling the compressor module 10 and can control control magnets 64 of the 2 / 2-way valves 46.The 2 / 2-way valves 46 of the compressed air collector 32 – in the example case, the air spring system 32 – correspond to the 2 / 2-way valve 60 shown in Figure 2a.
[0067] Ventilation
[0068] Regardless of whether the compressed air supply system 30 is operated in open or closed mode, venting one or more components—such as the bellows 34—of the compressed air receiver 32 may be necessary. In the case of a vehicle with an air suspension system, one or more bellows 36 of the air suspension system must be vented if the vehicle is to be lowered on one side or all sides.
[0069] The venting of the compressed air collector 32 – e.g., when lowering the vehicle with an air suspension system – can also occur in open or closed operating mode. These variants for venting the compressed air collector 32 are explained in more detail below. In both cases, the venting of the compressed air collector 32 is involved – not the venting of the compressed air supply system 30 as a whole. Venting the compressed air supply system 30 necessarily occurs in open operation, in which air from the compressed air supply system 30 is released into the environment.
[0070] Ventilation in open operation
[0071] For venting in open operating mode, the compressed air supply system 30 in the example shown is designed as an indirectly venting compressed air supply system.
[0072] For this purpose, a drain valve 50, a pneumatically controlled 3 / 2-way valve 70, throttles 80.1 and 80.2, and a further check or one-way valve 42.1 are provided - see the corresponding border 84 around the components for indirect venting in Figure 1. Venting of the compressed air supply system 30 and one or more compressed air consumers 32 can be effected in the open operating mode by opening the drain valve 50, which is also designed as an electrically controlled 2 / 2-way valve. Opening the drain valve 50 causes the pneumatically controlled 3 / 2-way valve 70, as also shown in Fig. 2b, to be moved into the working position. The working position is the position in which venting takes place.After the release valve 50 opens, the pressure of the air to be vented acts as a control pressure, acting on a control piston 74, which moves the 3 / 2-way valve 70 into the operating position against the force of its return spring 72. Throttle valves 80.1 and 80.2, as well as two check or one-way valves 42.1 and 42.2, effectively limit the control pressure for actuating the pneumatically controlled 3 / 2-way valve 70.
[0073] Ventilation in closed operation
[0074] In the closed operating mode, the components of the compressed air collector 32 are vented into the pressure vessel 36.
[0075] During venting in closed operating mode, the air is pumped from the bellows 34 into the pressure accumulator 36 by means of the compressor 12 and its second compressor stage 12.2. For this purpose, the compressor 12 is activated, and the check valve 48 and the reservoir valve 52 are opened. This allows, for example, the air suspension system 32 to be lowered in closed operating mode. The first stage 12.1 of the compressor 12 is pneumatically ineffective in this case.
[0076] Summary of open / closed operating mode
[0077] An open operating mode occurs when the compressor 12 supplies compressed air directly from the environment to the compressed air receivers
[0078] 34, for example, the bellows 34 of the air suspension 32; then the compressor 12 is activated, the separation valve 44 is activated, the bellows valves 46 are activated => request "Lift" the compressor 12 fills the compressed air reservoir 36 from the environment; then the compressor 12 is activated, the reservoir valve 52 is activated => request "Fill reservoir" the air from the compressed air consumers 34 (in the example: the bellows 34 of the air suspension system 32) is vented into the atmosphere (bellows valves activated, separation valve activated, drain valve activated) => request "Lower" into atmosphere
[0079] A closed operating mode exists when
[0080] The air is pumped from the bellows 34 into the pressure accumulator 36; then the compressor 12 is activated, the return valve 48 is activated, and the reservoir valve 52 is activated => "lower" request in closed operating mode ("reflow"). The first stage 12.1 of the compressor 12 is pneumatically ineffective in this case.
[0081] The air is pumped from the pressure accumulator 36 into the bellows 34; then the compressor 12 is activated, the boost valve 54 is activated, the separation valve 44 is activated, and the bellows valves 46 are activated => "lift" request in closed operating mode ("boost"). The first stage 12.1 of the compressor 12 is pneumatically ineffective in this case.
[0082] The compressor module
[0083] The compressor module 10 shown in Fig. 3 is intended for use in the compressed air supply system 30, as shown by way of example in Fig. 1 using a circuit diagram. The compressor module 10 is designed as a structural unit comprising the compressor 12, the electric motor 14, and the motor control (16, see Fig. 6; not shown in Fig. 1; typically flanged directly to the electric motor 14), as well as other components such as the air dryer 18 and the air distributor 20, etc.
[0084] Fig. 4 shows a sketch of the stator and rotor of a brushless DC motor. The sketched brushless DC motor 14, as a so-called internal rotor, typically has a stator 14.1 equipped with electromagnetic coils, a rotor 14.2 equipped with permanent magnets, and an electronic motor controller 16 (see Fig. 6). The motor controller 16 is configured as an electronic commutator such that the motor controller 16 controls the power supply to the coils 14.3 of the stator 14.1 via power switches and the terminals A, B, and C such that the coils 14.3 are periodically supplied with power in turn such that a rotating magnetic field is produced, which, via magnetic forces, causes a synchronous rotation of the rotor 14.2 equipped with permanent magnets.
[0085] For the known speed control of the brushless electric motor 14, the motor comprises means for detecting the rotor angle, e.g., a Hall sensor 14.4 for detecting the rotor position. This also allows a phase angle between the applied rotating field and the mechanical rotation of the rotor 14.2 to be detected, and the phase angle of the rotating field can be adjusted accordingly. Thus, the BLDC motor 14 behaves similarly to a mechanically commutated DC motor. However, as a brushless DC motor, it is more efficient, subject to less wear, and can be better speed-controlled than electric motors 14 with a brush commutator.
[0086] To generate the rotating field by periodically energizing the coils 14.3 via terminals A, B, and C, the motor control 16 is provided, which functions as an electronic commutator; see Fig. 6.
[0087] The speed of the electric motor 14 is also controlled in a conventional manner via the motor controller 16. For this purpose, a target speed is specified to the motor controller 16. An electronic control unit 100 is provided to specify the target speed. The electronic control unit 100 is supplied with a value for the average motor current by the motor controller 16 or is connected to a current sensor 58, 102 that detects the respective motor current consumed by the electric motor 14 during operation.
[0088] The current consumption of the electric motor 14 can be calculated by the motor controller 16 from the measured phase currents or measured directly using the current sensor 58 or 102. In the first case, three current sensors 102 are required, which are necessary anyway for operational reliability. In the second case, an additional current sensor 58 is required in the supply branch (see Figure 1). The variant without a separate current sensor 58 is therefore preferred.
[0089] Compared to an unregulated DC motor, regulated, brushless DC motors offer the advantage that their speed can be continuously controlled without additional design effort. The commutation of a brushless DC motor is electronic, whereas a DC motor with a brush-commutator system is mechanically commutated.
[0090] For acoustic reasons, air spring systems require a constant speed across the entire specified load range (voltage, back pressure and boost pressure, temperature, geodetic altitude), which argues in favor of using a controlled DC motor.
[0091] The disadvantage of the speed specification is that with the requirement n=const, the motor current increases with the torque and, in individual cases, can even exceed the defined maximum limit of 35A, for example. To comply with the maximum permitted current consumption, the compressor would have to be designed in such a way that the current consumption is never exceeded under worst-case operating conditions within the specified application cases. One such scenario could be a loaded vehicle, locked in terrain. It is proposed to design the motor for a constant speed as standard and to reduce the required drive power of the compressor if the permitted current consumption (usually 35A) is exceeded. For this purpose, the current current consumption of the compressor is determined; if the defined limit is exceeded, the closed operation of the compressor is terminated and the control is brought to an end in open operating mode.
[0092] The advantage of switching modes based on the average motor current is that the unit-specific tolerances, the different pressure ranges and other values that influence the current consumption of the electric motor - i.e. the motor current - do not have to be maintained in the form of worst-case assumptions, but are recorded unit-specifically and the performance of the compressor is maximized in all operating ranges.
[0093] Typically, the pneumatic performance of a compressor for an air suspension system is designed for the most common operating point. For example, a volume flow of 130 l / min is required at 11 bar boost pressure and 11 bar back pressure. The maximum current consumption of 35 A, however, applies across all operating ranges (operating and ambient pressures, voltages).
[0094] To avoid over-engineering the electric motor, it is designed for a current consumption of approximately 30A at the specified operating point (taking into account device variations, service life influences, and slightly higher operating loads). Particularly in supercharged operation, a sharp increase in the required drive power or current beyond 35A (current ~ torque) is observed with increasing backpressure.
[0095] In the example shown in Fig. 5, the current increases by more than 2A per bar of back pressure. A remedy would be to design the compressor module 10 in such a way that no current is exceeded in the defined, rather rare worst-case operating points. However, this has the disadvantage that the compressor module 10 exhibits a correspondingly reduced, non-specified performance in the frequently encountered operating ranges. A required flow rate of, for example, 130 l / min at 11 bar of inlet pressure and 11 bar of back pressure cannot be achieved in this case. The problem is exacerbated by device variation and service life influences. To avoid the high currents, the speed of the BLDC motor can be reduced. However, due to the proportionality of speed and current, this may result in an excessive, necessary speed reduction. For example, if the current consumption is to be reduced from 60A to 35A, the speed would have to be reduced to 58% of the original, from, for example, 2850rpm.1 to under 1700min' 1 This significant reduction in speed can lead to undesirable effects on airborne and structure-borne noise.
[0096] One approach is to operate the BLDC motor at a constant speed and, to avoid oversizing the DC motor, reduce this speed under certain load conditions (operating voltage and load). With correct design and correct consideration of all nominal conditions, the maximum current of, for example, 35A will not be exceeded. However, this requires that all current-influencing factors, such as component tolerances and operating temperatures, are considered in the form of worst-case assumptions, and that the resulting early switch to a lower speed (including the resulting performance reduction) is acceptable.
[0097] The aim was therefore not to design the compressor module for the rare worst-case conditions, but instead to provide a design according to the most common operating conditions in combination with a current limitation to ensure the specified current limits in conjunction with situationally maximum compressor performance.
[0098] The requirement for constant compressor speed leads to an increasing current consumption with increasing compressor drive torque (which is proportional to the required motor torque):
[0099] Formula: MX 27T X 71 = J] X [ / x / with:
[0100] M = Compressor drive torque (is constant at constant pressure) n = Compressor speed (is determined according to conventional control strategy at
[0101] BLDC kept constant)
[0102] T = efficiency
[0103] U = supply voltage (specified, between 9V and 16V as required)
[0104] / = Motor current (usually limited to 35A)
[0105] Measurements have shown that the motor current consumption of a supercharged compressor used in car air suspension systems can increase by more than 2 A / bar of back pressure. Thus, when designed for the nominal point of 11 bar boost pressure and 11 bar back pressure at I = 30 A, a back pressure of only 13.5 bar would be permissible (which would then no longer cover the entire required operating range up to 18 bar, for example). Further reductions can result from: manufacturing-related device variations, running-in effects
[0106] wear and tear
[0107] Ambient conditions Self-heating
[0108] For the inventive switching from the closed to the open operating mode when a predetermined maximum motor current is reached or exceeded, the current consumption of the drive motor 14 for the compressor 12 is continuously determined. As soon as the current consumption (i.e. the motor current) exceeds the predetermined limit for a certain period of time, the torque requirement of the compressor is reduced by switching to open operation. In the example shown, the motor current in charged operation reaches the current limit of 35A at a back pressure of approximately 11 bar. If the compressed air supply system 30 were to continue to be operated in the closed operating mode, the electric motor 14 for driving the compressor 12 would draw a motor current of 48A. By switching to the open operating mode, on the other hand, the current consumption of the electric motor 14 drops to approximately 19A, although of course with a correspondingly reduced volume flow.This is shown in Figure 7.
[0109] The compressor module 10 is advantageously designed so that it can handle the majority of operating conditions without switching modes. Only worst-case operating conditions such as maximum payload plus maximum ride height or high axle articulation should result in a corresponding switch to open operation.
[0110] Furthermore, the basic design of the compressor 12 and the associated electric motor 14 - i.e. the compressor module 10 - when using the invention should not be based on worst case tolerance levels, etc., but should also be analogous to the nominal values.
[0111] Advantages also arise in the event that the nominal diameters on the compressor pressure side are temporarily too small (e.g. when conveying into only one bellows 34) and an excessive back pressure builds up due to the high delivery volume flow, which in turn would lead to an excessively high motor current.
[0112] The application of the switching from a closed to an open operating mode according to the invention is not limited to compressors driven by a BLDC DC motor (although the latter are preferred), but can also be extended to compressors with other DC motors.
[0113] In the example case, switching from closed to open operation is carried out as described below.
[0114] Switching from boost lifting (i.e., from closed operating mode) to open operating mode is very simple by deactivating (and thus closing) boost valve 54. During reflow lowering activities (i.e., when venting in closed operating mode, e.g., to lower the vehicle), switching to open operating mode is somewhat more complex, as compressor 12 must be shut down, return valve 48 and reservoir valve 52 must be closed, and drain valve 50 must be opened. Therefore, predictive control is advantageous here, as explained below.
[0115] For predictive control, not (only) the motor current is determined, but also the pressure P on the pressure side of the compressor 12 or in the pressure accumulator 36. For this purpose, at least one PU converter is provided as a pressure sensor 78. This can be provided, for example, on the main pressure line 40 or the pressure accumulator 36, or at both locations, or even at other locations, depending on which pressure is to be measured, for example, for predictive control.
[0116] The accuracy of the prediction of the motor current IB, pra and thus the decision whether, for example, a sink occurs in the open or closed operating mode, can be improved over the following cases 1 to 3 by increasing the prediction complexity.
[0117] Since the motor current is proportional to the drive torque required by the compressor (torque requirement), the selection of the open operating mode or the closed operating mode can be made by predictive control without considering the motor current itself, but solely based on the influencing variables that influence the torque requirement of the compressor at a given speed and their foreseeable temporal development - for example, the counterpressure that increases as the pressure accumulator fills. This - the predictive selection of the open or closed operating mode and the corresponding control of the compressed air supply system - represents an independent inventive concept that can be implemented both in combination with the mode switching based on the motor current described here and independently of the motor current.
[0118] In the simplest case 1, the compressed air control is designed to activate either the closed operating mode or the open operating mode in response to a "lowering" request, depending solely on the current accumulator pressure (i.e., the air pressure in the accumulator). If the current accumulator pressure is too close to a maximum permissible accumulator pressure limit, so that not enough additional air mass can be deposited in the accumulator to release sufficient air from the air receiver (e.g., to lower the vehicle far enough), then open operation is selected from the start to avoid switching the operating mode during lowering. For this purpose, the compressed air control is designed, among other things, as a pressure estimator.
[0119] In the second case, the compressed air control system is designed to calculate the resulting (i.e., expected) accumulator pressure in advance (air mass manager) based on the available information about accumulator pressure and volume, bellows pressure, bellows geometry, and height, as well as the requested control (e.g., raising or lowering), or to estimate it if the data is incomplete (air mass estimator). If the calculated or estimated accumulator pressure exceeds a specified or learned accumulator pressure limit, the lowering process is carried out from the outset by venting the bellows to atmosphere, i.e., in open operating mode. No switching occurs during the lowering process.
[0120] In a third, advantageous embodiment, the compressed air control is designed to adaptively determine a pressure limit from case 2, but also from case 1, based on a correlation between backpressure and current consumption learned during operation of the compressor module 10. Here, the unavoidable device tolerances are compensated for by switching on a compressor-specific basis in the form of self-calibration. Reference symbol (part of the description)
[0121] 10 Compressor module
[0122] 12 Compressor
[0123] 12.1 first compressor stage
[0124] 12.2 second compressor stage
[0125] 14 Electric motor
[0126] 14.1 Stator
[0127] 14.2. Rotor
[0128] 14.3 Coil
[0129] 14.4. Hall sensor
[0130] 16 electronic engine control (engine electronics)
[0131] 18 air dryers
[0132] 20 air distributors
[0133] 22 Compressed air line (general)
[0134] 30 Compressed air supply system
[0135] 32 air suspension system
[0136] 34 bellows of the air springs
[0137] 36 pressure accumulators
[0138] 38 air dryers
[0139] 40 Main pressure line (special compressed air line)
[0140] 42 One-way valve / check valve
[0141] 44 Separation valve (electrically controlled)
[0142] 46 Pressure sensor valve (bellows valve, electrically controlled)
[0143] 48 Check valve (electrically controlled)
[0144] 50 Drain valve (exhaust valve, electrically controlled)
[0145] 52 Reservoir valve (electrically controlled)
[0146] 54 Boost valve (electrically controlled)
[0147] 56 Compressed air control
[0148] 58 Current sensor
[0149] 60 2 / 2-way valve (electrically controlled)
[0150] 62 return spring
[0151] 64 Control solenoid 70 3 / 2-way valve (pneumatically controlled) for indirect venting
[0152] 72 return spring
[0153] 74 control pistons
[0154] 76 Boost and return line
[0155] 78 Pressure sensor; PU converter
[0156] 80 Throttle
[0157] 82 components for closed operation
[0158] 84 components for indirect ventilation
[0159] 90 memory for operating specifications
[0160] 92 Current signal input
[0161] 94 Pressure signal input for a signal representing the pressure in the pressure accumulator 36
[0162] 96 Pressure signal input for a signal representing the pressure of the compressed air in the main pressure line of the compressed air supply system
[0163] 98 Pressure signal input for a signal representing the pressure of the compressed air at the compressed air receiver
[0164] 100 electronic control unit
[0165] PAbn Pressure of the compressed air at the compressed air receiver
[0166] SpAbn signal representing the pressure of the compressed air at the compressed air receiver
[0167] PAni Pressure of the compressed air in the main pressure line of the compressed air supply system
[0168] SpAni signal representing the pressure of the compressed air in the main pressure line of the compressed air supply system
[0169] PR pressure of the compressed air in the pressure accumulator
[0170] PR limit Accumulator pressure limit, limit for the pressure of the compressed air in the pressure accumulator
[0171] PR estimated pressure of the compressed air in the pressure accumulator
[0172] SPR signal representing the pressure of the compressed air in the pressure accumulator n S oii Target speed (operating specification)
[0173] IB Signal representing motor current
[0174] SIB the motor current
[0175] SAnf Request signal V Volume of a compressed air consumer, especially an air spring h Height of a compressed air consumer, especially an air spring
Claims
Patent claims 1 . Compressed air supply system (30), in particular for a motor vehicle, comprising: one or more compressed air consumers (32; 34), compressed air lines (40), electrically controllable valves (44, 46, 48, 50, 52, 54), a compressed air control (56) for controlling the electrically controllable valves (44, 46, 48, 50, 52, 54), a compressor (12) with an electric motor (14) as a drive, and a pressure accumulator (36), wherein the compressed air consumer(s) (32; 34) are or can be connected pneumatically to the compressor (12) and / or the pressure accumulator (36) via the compressed air lines (22) and the electrically controllable valves (44, 46, 48, 50, 52, 54) in such a way that the compressed air supply system (30) can be operated either in an open operating mode or in a closed operating mode, 14) characterized in that the compressed air control (56) has a current signal input (90) for a current signal (Si),which represents a motor current (IB) received or to be received by the electric motor (14) driving the compressor (12), wherein the compressed air control (56) is designed to control the electrically controllable valves (44, 46, 48, 50, 52, 54) in accordance with the open operating mode of the compressed air supply system (30) when a current signal (SIB) is present at the current signal input (92) that represents an average motor current (IB) whose magnitude is equal to or greater than a predetermined maximum value (Imax) for the motor current.
2. Compressed air supply system (30) according to claim 1, characterized in that the current signal input (92) is connected to at least one current sensor (58, 102) which is designed to detect one of the electric motor (14) driving the compressor (12) to detect the motor current (IB) ZU and to output a signal (SIB) representing this to the compressed air control (56).
3. Compressed air supply system (30) according to claim 1 or 2, characterized in that the compressed air consumer (32) is an air spring system (32) with one or more bellows (34).
4. Compressed air supply system (30) according to at least one of claims 1 to 3, characterized in that the compressor (12) is combined with the electric motor (14) to form a structural unit (10).
5. Compressed air supply system (30) according to at least one of claims 1 to 4, characterized in that the electric motor (14) is a speed-controlled BLDC motor and has at least one target speed (n S oii) is specified.
6. Compressed air supply system (30) according to at least one of claims 1 to 5, characterized in that the compressed air control (56) is designed to predictively determine a motor current (Iß pra) to be absorbed by the electric motor (14) on the basis of an air pressure (PA ) in the compressed air supply system (30) and a request (SAnf) - in particular a "lower" request (SANF lower) - to the compressed air consumer (32; 34) and to cause a switchover to open operation when the predictively determined motor current (Iß pra) reaches or exceeds the specified maximum value (Ißmax) for the motor current.
7. Compressed air supply system (30) according to claim 6, characterized in that the compressed air supply system (30) has a pressure sensor (78) which is arranged and designed such that it detects an air pressure (PAni) prevailing in the compressed air supply system (30) during operation and outputs a pressure signal (SpAni) representing this pressure to the compressed air control (56).
8. Compressed air supply system (30) according to at least one of claims 1 to 7, characterized in that the compressed air supply system (30) has a reservoir valve (52) which is arranged pneumatically between the pressure accumulator (36) and a pneumatic main pressure line (40).
9. Compressed air supply system (30) according to at least one of claims 1 to 7, characterized in that the compressed air supply system (30) has a boost valve (54) which is pneumatically arranged between the pressure accumulator (36) and a boost and return line (76).
10. A method for operating a compressed air supply system (30), in particular for a motor vehicle, comprising: one or more compressed air consumers (32; 34), compressed air lines (40), electrically controllable valves (44, 46, 48, 50, 52, 54), a compressed air control (56) for controlling the electrically controllable valves (44, 46, 48, 50, 52, 54), a compressor (12) with an electric motor (14) as a drive, and a pressure accumulator (36), wherein the compressed air consumer(s) (32; 34) are or can be connected pneumatically to the compressor (12) and / or the pressure accumulator (36) via the compressed air lines (40) and the electrically controllable valves (44, 46, 48, 50, 52, 54) in such a way that the compressed air supply system (30) can be operated either in an open operating mode or in a closed operating mode, characterized in that a current signal (SIB) is supplied to the compressed air control (56) during operation, which current signal represents a motor current (IB) received or to be received by the electric motor (14) driving the compressor (12), and the compressed air control (56) switches the compressed air supply system (30) from the closed to the open operating mode and controls the electrically controllable valves (44, 46, 48, 50, 52, 54) in accordance with the open operating mode of the compressed air supply system (30) when a current signal (SIB) is present at the current signal input (92) which represents an average motor current (IB) whose magnitude is equal to or greater than a predetermined maximum value (temax) for the motor current.
11. Method according to claim 10 for operating a compressed air supply system (30) having a boost valve (54) pneumatically connected to the pressure accumulator (36), wherein the switching from the closed operating mode to the open operating mode occurs when compressed air is supplied to the pressure consumer (32) by deactivating the boost valve (54).
12. Method according to claim 10 or 11 for operating a compressed air supply system (30) which has a discharge valve (50), a return flow valve (48) and a reservoir valve (52) which is pneumatically connected to the pressure accumulator (36), wherein the switching from the closed operating mode to the open operating mode when compressed air is discharged from the pressure sensor (32) is carried out by switching off the compressor (12), closing (deactivating) the return flow valve (48) and the reservoir valve (52) and opening (activating) the discharge valve (50).
13. Method according to claim 10 or 11 for operating a compressed air supply system (30) which has a pressure sensor (78) on the compressed air reservoir (36) and a drain valve (50), a return valve (48) and a Reservoir valve (52) which is pneumatically connected to the pressure accumulator, wherein the compressed air control (56), in the event that compressed air is to be discharged from the pressure sensor (32), activates the closed operating mode when the current accumulator pressure in the pressure accumulator (36) is less than an accumulator pressure limit value (PR limit), or activates the open operating mode when the current accumulator pressure (PR) in the pressure accumulator (36) is equal to or greater than an accumulator pressure limit value (PR limit).
14. Method according to claim 10 or 11 for operating a compressed air supply system (30) which has a pressure sensor (78) on the compressed air reservoir (36) and a drain valve (50), a return flow valve (48) and a reservoir valve (52) which is pneumatically connected to the pressure reservoir (36), wherein the compressed air control (56) is designed for the case that compressed air is to be discharged from the pressure consumer (32) on the basis of the available information about the reservoir pressure in the pressure reservoir (36) and the volume of the pressure reservoir (36), the pressure (PAbn) in the compressed air consumer (32;34) or one or more of its components (34) and their volumes (V) and height (h) to calculate or estimate in advance the expected accumulator pressure (PR), and in the event that the calculated or estimated accumulator pressure (PRgesch) exceeds a predetermined accumulator pressure limit value (PR grenz), to activate the open operating mode by switching off the compressor (12), closing (deactivating) the return valve (48) and the reservoir valve (52) and opening (activating) the drain valve (50); 15. Method according to one of claims 12 to 14, wherein the compressed air control (56) adaptively determines the accumulator pressure limit value (PR limit) from a correlation of back pressure (PA ) and current consumption (IB) learned during operation of the compressor module (10).