Compressor module, compressed-air supply system, and method for operating a compressed-air supply system having the compressor module
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
Compressor modules in vehicle compressed air supply systems face challenges in providing reliable and environmentally friendly operation, especially under unfavorable conditions, as brushless DC motors require higher current consumption with increased mechanical load, potentially leading to overload of the on-board electrical system.
A compressor module with a speed-controlled brushless electric motor and an electronic control unit that specifies two target speeds based on average motor current, reducing power output and preventing overload by switching to a lower target speed when the average motor current exceeds a predetermined limit, thereby protecting the electrical system and optimizing acoustic performance.
This solution effectively reduces power delivery and prevents electrical system overload while maintaining efficient operation, using existing motor electronics and minimizing control effort, and avoids frequent speed changes, ensuring robust and simple control of the compressor module.
Smart Images
Figure EP2024061314_14112024_PF_FP_ABST
Abstract
Description
[0001] Compressor module, compressed air supply system and method for operating a compressed air supply system with the compressor module
[0002] The invention relates to a compressor module, in particular a compressor module for a compressed air supply system of a vehicle. The invention also relates to a compressed air supply system for a motor vehicle with the compressor module and, in addition, to a method for operating the compressed air supply system with the compressor module and a speed-controlled electric motor for driving the compressor.
[0003] Compressor modules are used, for example, for compressed air supply systems in motor vehicles. In motor vehicles, compressed air supply systems can supply compressed air to, for example, an air suspension system with air springs as compressed air consumers and / or a pneumatic braking system with air brakes as compressed air consumers. 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. Compressors and compressors are used synonymously in this description and refer to units that compress air.
[0004] Brushless DC motors (BLDC motors: Brushless Direct Current motors) are preferably used as electric motors for driving compressors. A brushless DC motor, as a so-called internal rotor, typically has a stator equipped with electromagnetic coils, a rotor equipped with permanent magnets, and motor electronics. The motor electronics are configured as an electronic commutator in such a way that the motor electronics controls the power supply to the stator coils (hereinafter also referred to as stator coils) via power switches in such a way that the stator 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 sinusoidally 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 (e.g. three or n times three) stator coils is digitally switched, i.e. either no current or the full current is supplied to the windings of the respective stator coil or stator coils of a phase. With sinusoidal commutation, each stator coil of the motor is supplied with a sine wave offset by 120°, resulting in a continuously rotating stator magnetic field of constant strength.
[0005] 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.
[0006] 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 – i.e., the brushless DC motor – poses a particular challenge. This includes, among other things, the fact that the compressor module must provide sufficient compressed air even under unfavorable conditions, which only rarely occur (H / DRSF-case operation). To achieve this, the drive, i.e., the brushless DC motor, must also be designed accordingly. For a given supply voltage of the brushless DC motor, a higher mechanical load – i.e., a higher mechanical output power – inevitably leads to a higher current consumption of the brushless DC motor.However, to protect the vehicle's electrical system, the maximum current consumption of a brushless DC motor must be limited.
[0007] 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.
[0008] The invention is based on the object of ensuring reliable and environmentally friendly operation of a compressor module in the simplest possible way.
[0009] To achieve this object, a compressor module according to claim 1 is proposed, in particular for a compressed air supply system of a vehicle. The compressor module has a compressor and a speed-controlled brushless electric motor for driving the compressor, during the operation of which a motor current IB occurs. Motor electronics with an electronic commutator and speed control are assigned to the speed-controlled brushless electric motor. According to the invention, the compressor module is connected to or has an electronic control unit, wherein the electronic control unit is designed to predetermine one of at least two different target speeds for the electric motor as a function of the average motor current IB, namely at least a predefined first target speed m. soii and a predefined second target speed n2, son, which is lower than the predefined first target speed m.soii, and to switch from specifying the predefined first target speed m , son to specifying the predefined second target speed n2, son when the average motor current IB reaches or exceeds a, in particular a first predetermined motor current limit value Imax.
[0010] The criterion for reducing the speed is preferably not the instantaneous value of the motor current, but an average motor current that represents the short-term average value of the motor current, so that a speed reduction is not triggered by a short-term current peak or cyclical fluctuations in the instantaneous value of the motor current.
[0011] The proposal is not only to design the motor as standard for at least two constant speeds depending on the operating voltage and torque requirement (which corresponds to the air pressure to be generated), but also to introduce a functional target current specification or limitation as an alternative, advantageous control variable, preferably additively. A suitable, voltage-dependent current limitation, which can also be specified by the vehicle, can protect the on-board electrical system and provide situation-dependent overload protection. The result is a superimposed, current-dependent target speed specification that takes the applicable current limits into account.
[0012] By specifying a lower predefined second target speed in the case in which the average motor current reaches or exceeds a predetermined motor current limit, e.g. the first motor current limit, an effective reduction in the output power and thus also an effective reduction in the average motor current consumed by the brushless electric motor is brought about and thus an overload of the brushless electric motor and / or the on-board network is effectively avoided using simple means, because this solution uses the motor electronics with electronic commutator and speed control that are already present in a brushless electric motor and beyond this only requires an extremely low control effort that can easily be achieved using simple means.At the lower predefined second target speed, the brushless electric motor of the compressor module can deliver a higher torque required in special load cases without exceeding the specified motor current limit.
[0013] The proposed solution offers the advantage that the measured variable for the limit value—namely, the specified motor current limit—which triggers the specification of a lower, predefined second target speed, is easy to record. This allows the electronic control unit to be designed simply and robustly with regard to controlling the compressor module. The action to be taken when the limit value is reached—namely, the specification of a lower, predefined second target speed—is also simple and can be implemented without any effort, especially because the existing motor electronics of the brushless electric motor can be used for this purpose.
[0014] A further positive effect is that frequent speed changes of the brushless electric motor are avoided and thus the compressor module can also be acoustically optimized for a few speed ranges.
[0015] The invention includes the recognition that a disadvantage of speed specification is that the requirement for a constant target speed n (n=const) results in a motor current that increases with the load torque, which in individual cases can even exceed the defined maximum limit for the absorbed motor current IB of, for example, 35A. Specifying a target speed for speed control based on the average motor current has the advantage that unit-specific tolerances, different temperatures and other values that influence the motor current do not have to be maintained in the form of worst-case assumptions, but can be recorded independently of the specific unit, and changes in the specified speed can thus be reduced to the minimum necessary.
[0016] The proposed solution is simpler than the known solution of designing the electric motor by default for at least two constant speeds depending on the operating voltage and torque requirement (the torque requirement depends on the pressure level the compressor is to generate). In addition to the known solution, specifying at least one current limit for the average motor current as a criterion for the transition from a higher first to a lower predefined second target speed can be provided as an alternative, advantageous load-dependent control.
[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, more than two target speeds are specified and the control unit is preferably designed to be able to rely on the specification of a predefined higher target speed n x , rather than specifying a predefined lower target speed (n x+i, son) when the average motor current (IB) reaches or exceeds one or a corresponding predefined motor current limit value (Imaxi Imax, red). This variant has the advantage that the reduction in the setpoint speed and thus also the reduction in the power delivered by the compressor module can take place in smaller steps so that the jumps in speed and power are not too great. According to one design variant, exactly one motor current limit value is specified. When this is reached for the first time in a load case, the setpoint speed is reduced from the predefined first setpoint speed to the lower predefined second setpoint speed.If, during operation at the lower predefined second setpoint speed, the load—and thus the torque to be delivered—increases to such an extent that the specified (first and only) motor current limit is reached again, the setpoint speed can be further reduced from the second predefined setpoint speed to an even lower third predefined setpoint speed. Depending on the degree of the respective reduction in the setpoint speed, several predefined setpoint speeds can be specified.
[0019] Preferably, the compressor module is designed such that it can be supplied with different supply voltages, wherein the control unit is configured to apply different predefined motor current limit values (Imax; Imax,red) for the different supply voltages. It is particularly advantageous if the control unit is configured to apply motor current limit values Imax,red for supply voltages Uv whose respective voltage values are below a limit voltage value Uv limit, which are lower than a predefined maximum motor current limit value Imax. For example, the compressor module can be designed such that it can be supplied with at least two supply voltages of different levels.Then, the control unit is designed to specify predefined motor current limit values for the at least two different supply voltages in such a way that the motor current limit values predefined for the at least two different supply voltages are different from one another.
[0020] Preferably, the maximum motor current limit value is adjustable to one of at least two different maximum motor current limit values.
[0021] The electric motor preferably has an electrically commutable stator, a permanently excited rotor, and the motor electronics preferably form a speed-controlled electronic commutator which generates an electric rotating field for the electric motor according to a predetermined target speed n S oii generated.
[0022] The compressor module preferably has a current sensor for detecting the motor current IB drawn by the electric motor, as well as an analog-to-digital converter for converting an output value supplied by the current sensor into a digital signal representing the average motor current IB drawn by the electric motor. The current sensors of the motor electronics, which are usually provided for each phase, can serve as current sensors. The average motor current can be determined by the motor electronics on the compressor module or by the compressed air control system. For example, the motor electronics can determine the average motor current from the three measured phase currents. Alternatively, an additional current sensor could also be provided.
[0023] The average motor current is a value of the motor current averaged over a period of a few seconds and / or low-pass filtered. By calculating a short-term average of the motor current or low-pass filtering the motor current, short-term peak values of the motor current are prevented from causing a reduction in speed. To transmit the motor current value, the compressor module has an interface through which the digital signal representing the motor current drawn by the electric motor can be retrieved during operation. The calculation of a value for the average motor current can already take place in the compressor module.
[0024] Furthermore, it is advantageous if the electric motor is designed such that it can deliver a maximum expected torque down to a supply voltage of 11.5 V without exceeding the specified motor current limit. In this way, unnecessarily frequent switching to a lower target speed can be avoided. A further aspect of the invention relates to a compressed air supply system according to claim 9. The compressed air supply system for a motor vehicle comprises: a compressor module, at least one compressed air consumer, in particular an air suspension system or a brake system, a compressed air reservoir, controllable valves, and a compressed air control unit for controlling the valves.
[0025] Preferably, the compressed air supply system is designed in such a way that it can be switched between open operation and closed operation.
[0026] A further aspect of the invention relates to a method according to claim 11. The method for operating a compressed air supply system with a compressor and a speed-controlled electric motor for driving the compressor comprises the steps:
[0027] Specifying a predefined first target speed, regularly or continuously comparing a current value of the average motor current with a predefined maximum motor current limit, and
[0028] Specifying a predefined second target speed that is lower than the predefined first target speed as soon as a current value of the average motor current is greater than or equal to the predefined maximum motor current limit.
[0029] The concept of the invention is not limited to a compressed air supply system or a compressed air consumer of a vehicle, such as air springs of an air suspension system or compressed air brakes of a braking system, comprising a compressor for generating compressed air using a controlled brushless electric motor. Rather, the method underlying the invention serves as a general method for operating controlled brushless electric motors at constant speeds in various load ranges.
[0030] 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, nor is it limited to an object that would be limited compared to the object claimed in the claims. In the case of specified dimensioning ranges, values within the stated limits are also intended to be disclosed as limit values and can be used and claimed as desired.
[0031] Further advantages, features and details of the invention will become apparent from the following description of the preferred embodiments and from the drawing, which shows:
[0032] Fig. 1 a compressor module with compressor, electric motor and motor electronics;
[0033] Fig. 2 shows a circuit diagram of an example of a compressed air supply system including compressed air consumers in the form of air springs of a vehicle; Fig. 3 shows symbols for the valves shown in Fig. 2 to explain their function;
[0034] Fig. 4 is a sketch illustrating the operation of a brushless electric motor;
[0035] Fig. 5 a symbolic representation of a compressor and a brushless electric motor with motor electronics driving it;
[0036] Fig. 6 is a diagram illustrating the prior art switching from a predetermined higher target speed to an assigned lower target speed as a function of operating voltage and load;
[0037] Fig. 7a is a diagram illustrating the switching according to the invention from a predetermined higher target speed to an assigned lower target speed when a predetermined motor current limit value is reached;
[0038] Fig. 7b is a diagram illustrating a variant of the switching according to the invention from a predetermined higher target speed to an assigned lower target speed when a predetermined motor current limit value is reached;
[0039] Fig. 8 is a diagram illustrating a further variant of the switching according to the invention from a predetermined higher target speed to an assigned lower target speed when a predetermined motor current limit value is reached;
[0040] Fig. 9 is a diagram illustrating a further variant of the switching according to the invention from a predetermined higher target speed to an assigned lower target speed when a predetermined motor current limit is reached; and Fig. 10 is a diagram illustrating a further variant of the switching according to the invention from a predetermined higher target speed to an assigned lower target speed when a predetermined motor current limit is reached.
[0041] A compressor module 10 can be designed as a structural unit comprising compressor 12, electric motor 14 and motor electronics (16, see Fig. 5; not shown in Fig. 1; typically flanged directly to the electric motor 14) as well as other components such as air dryer 18 and air distributor 20 etc., see Fig. 1 .
[0042] The compressor module 10 is intended for use in a compressed air supply system 30, as shown by way of example in Fig. 2 using a circuit diagram. The compressed air supply system 30 serves, for example, to supply compressed air to an air suspension system 32 comprising several air springs 34 of a vehicle. Instead of an air suspension system, other compressed air consumers, e.g., compressed air brakes of a compressed air brake system, can also be pneumatically connected to the compressed air supply system 30.
[0043] The compressed air supply system 30 shown in Fig. 2 can be operated in an open or a closed mode. In open mode, outside air is sucked in from the environment and compressed (see the dashed arrow in Fig. 2), and in closed mode, air is taken from a pressure vessel 36 - also referred to here as a reservoir - and compressed (see the dotted arrow in Fig. 2). In open mode, the outside air is first pre-compressed in two stages by compressor 12.1 and then post-compressed by compressor 12.2. Since the air in pressure vessel 36 already has a higher static pressure than the outside air in the environment, in closed mode the air is only post-compressed by compressor 14.2.
[0044] In both cases, the compressed air is finally fed via an air dryer 38 to a pneumatic main pressure line 40 and through a one-way or check valve 42.2 and thus made available for delivery to an air spring system 34 or fed to the pressure vessel 36.
[0045] The compressed air is delivered to the air spring system 32 or the compressed air reservoir 36 and distributed within the air spring system 32—in the example, between the air springs 34 of the air spring system 32—by means of electrically controlled 2 / 2-way valves 50, one of which is also shown in Fig. 3a. In their first (rest) position, which is effected by a return spring 42, the 2 / 2-way valves 50 act as one-way or check valves. In the controlled second (working) position, the 2 / 2-way valves 50 are open. The electrically controllable 2 / 2-way valves 50 are connected to an electronic control unit (not shown), which can be identical to an electronic control unit for controlling the compressor module 10 and can control control magnets 54 of the 2 / 2-way valves 50.
[0046] Venting of the compressed air supply system 30 and the spring system 32 can be achieved by opening a vent valve 56, which is also designed as an electrically controlled 2 / 2-way valve. Opening the vent valve 56 causes a pneumatically controlled 3 / 2-way valve 60, as shown in Fig. 3b, to be moved into the working position. The working position is the position in which venting occurs. The pressure of the air to be vented acts as a control pressure acting on a control piston 54, which moves the 3 / 2-way valve 60 into the working position against the force of its return spring 52. Throttle valves 70.1 and 70.2 as well as an additional check or one-way valve 42.2 effectively limit the control pressure for controlling the pneumatically controlled 3 / 2-way valve 60.
[0047] 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 motor electronics 16 (see Fig. 5). The motor electronics 16 are configured as an electronic commutator such that the motor electronics 16 controls the power supply to the stator coils 14.3 of the stator 14.1 via power switches and terminals A, B, and C such that the stator coils 14.3 are periodically supplied with power in turn, creating a rotating magnetic field that, via magnetic forces, causes synchronous rotation of the rotor 14.2 equipped with permanent magnets.
[0048] For the known speed control of the brushless electric motor 14, the latter has 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 to be determined.
[0049] 14.2, and the phase angle of the rotating field is 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, less prone to wear, and can be better controlled in speed than electric motors with a brush commutator.
[0050] To generate the rotating field by periodically energizing the stator coils
[0051] 14.3 The motor electronics 16, which functions as an electronic commutator, is provided via terminals A, B, and C; see Fig. 5.
[0052] The speed of the electric motor 14 is also controlled in a conventional manner via the motor electronics 16. For this purpose, a target speed is specified to the motor electronics 16. An electronic control unit 100 is provided to specify the target speed. The control unit receives a value for the average motor current from the motor electronics 16 or is connected to a current sensor 102 that detects the respective motor current consumed by the electric motor 12 during operation.
[0053] The current consumption of the electric motor 12 can be calculated by the motor electronics 16 from the measured phase currents or measured directly using a current sensor. In the first case, three current sensors are required in the motor electronics, which are necessary for operational reliability anyway. Therefore, the variant without a separate current sensor is preferred.
[0054] The electronic control unit 100 is configured such that, depending on the average motor current IB, one of at least two different target speeds for the electric motor 14 is determined and / or specified, namely at least one predefined first target speed m. soii and a predefined second target speed n2, son, which is lower than the predefined first target speed ni , son, and to switch from specifying the predefined first target speed m . soii to specifying the predefined second target speed n2, son when the average motor current IB reaches or exceeds a specified motor current limit value Imax or I max, red.
[0055] The compressor module 10 has at least one current sensor 102 for detecting the motor current IB drawn by the electric motor 14, as well as an analog-to-digital converter 104 for converting an output value supplied by the current sensor 104 into a digital signal representing the motor current IB drawn by the electric motor 14. The digital signal representing the motor current drawn by the electric motor can be retrieved during operation via an interface 106. The motor current IB represented by the digital signal is preferably already a time-averaged or low-pass filtered motor current.
[0056] Fig. 6 illustrates the switching from a given higher target speed nnominal to an assigned lower target speed n re d, stat, when a predetermined supply voltage U is undershot, as is known from WO 2020 / 225024 A1.
[0057] Depending on the efficiency of the respective electric motor, the current technology allows for a switchover to the lower target speed even before the maximum permissible motor current is reached. For example, if a switchover occurs at a supply voltage of 12V, the least efficient electric motor will already have the maximum permissible motor current, while more efficient electric motors will only draw a significantly lower motor current at this supply voltage and load.
[0058] Specifically, Fig. 6 illustrates that a "worst efficient compressor" WoCo would exhibit the maximum permissible current consumption at a supply voltage of <=12V, thus requiring a speed reduction at 12V. A "mean efficient compressor" MeCo would exhibit the maximum permissible current consumption at a supply voltage of <=11V, thus requiring a speed reduction at 11V. A "most efficient compressor" MoCo would exhibit the maximum permissible current consumption at a supply voltage of <=10.5V, thus requiring a speed reduction at 10.5V.
[0059] The solution proposed in WO 2020 / 225024 A1 requires switching to the lower speed depending on load and supply voltage, so that a "worst-efficient compressor" cannot exceed the maximum motor current. All "better" compressors thus switch to the second, lower speed earlier than necessary, leading to an avoidable reduction in compressor performance in the vehicle.
[0060] If the nominal conditions are temporarily exceeded or the customer requires lower maximum currents depending on the situation, the approach from WO 2020 / 225024 A1 alone is also not sufficient.
[0061] In general, the requirement for constant compressor speed with decreasing compressor supply voltage U or with increasing mechanical load (compressor drive torque M) leads to an increasing compressor current, because the mechanical power of the compressor module and the absorbed electrical power are related as follows:
[0062] M x 2 X n = r] XUX / with:
[0063] M = compressor drive torque (= constant at constant pressure) n = compressor speed (= constant specified and controlled) r| = motor efficiency
[0064] U = supply voltage (variable from 9V to 16V as required)
[0065] I = motor current
[0066] The supply voltage is the voltage of the vehicle's electrical system and is typically between 9V and 16V. The maximum permissible motor current is limited to 35A, for example, by specifications.
[0067] The upper diagram of Fig. 7 (Fig. 7a) shows the current I increasing with decreasing voltage U. In the example, the current I reaches the limit Imax at a voltage of 11V (point (1 )), the compressor speed n constantly corresponds to the first set speed nnominai, corresponding to m, son.
[0068] The solution known from WO 2020 / 225024 A1 provides for a supply voltage of 11V (point 1 ) to a second, reduced speed n2, son (also known as n r ed, stat). If the operating voltage U drops further, the current consumption of the electric motor, initially reduced by the speed reduction, increases again. At 9 V, Imax is then reached again (point 1 a).
[0069] In this state of the art technology, the voltage limit for speed reduction is statically set via parameterization, in the example at 11V, and applies equally to all operating conditions and compressors.
[0070] In the switching according to the invention depending on a predetermined motor current limit value, the operating voltage at which switching to the lower target speed occurs is variable.
[0071] Fig. 7a and Fig. 7b illustrate how a motor current limit can be meaningfully specified and what effects this has on the operating behavior of the electric motor. Fig. 7a illustrates a first case in which the resulting current value Imax is greater than the limit value specified by the user due to, for example, variation, rare operating conditions, etc. In this case, Imax is the current that occurs under the current operating conditions for the compressor currently in use, Imax, red is the maximum current statically permitted by the user. The hatched areas indicate operating conditions that would then violate the permissible current consumption according to the user's specifications.
[0072] Fig. 7a illustrates a first case in which the user requests a low limit value Imax, red depending on the situation or specifically for a specific vehicle, which can also be dynamically specified.
[0073] Here, compliance with the defined current limit is ensured by implementing additional target speeds, in the example below the speeds n re d, stat_i and n re d, stat_2. According to the embodiment shown in Fig. 7b, three speed ranges are defined, resulting in two switching voltages.
[0074] However, since switching does not occur as a function of a predetermined (switching) voltage, but rather as a function of the average motor current, the electric motor can be operated significantly more efficiently. If, for example, the compressor's power consumption (and thus the required motor current) decreases due to operation at an altitude of 3000 m, the approach allows the first target speed to be maintained from nominal down to significantly lower operating voltages. In the example in Fig. 8, the current consumption during operation at an altitude of 3000 m is shown by a solid line. Applying the current limit Imax, red, a one-time speed reduction at 9.8 V is sufficient to avoid exceeding the maximum current.
[0075] Fig. 8 also illustrates, using the dashed saw-speed line, how corresponding target speeds and associated speed jumps can be provided to reduce the adaptive speed selection. For example, the first target speed nnominai (ni, son) can be 3000 rpm, and the reduced second target speed n re d, stat_i (02, son) can be 2800 rpm, the further reduced third target speed n re d, stat_2 (ns. soii) can be 2600 rpm and an even further reduced fourth target speed n re d, stat_3 (n4, son) can be 2400 rpm.
[0076] Examples of further advantageous embodiments are shown in Figures 9a, 9b and 10.
[0077] To protect the vehicle electrical system, a reduction of the maximum permissible compressor current can be provided depending on the vehicle electrical system voltage, i.e. a reduced motor current limit value Imax, red is defined as a function of the operating voltage provided by the vehicle electrical system:
[0078] Imax, red = f(supply voltage U).
[0079] Such a reduction in the motor current limit can be requested by a central vehicle control unit or implemented independently by a compressor control unit. Figures 9a and 9b show an example of a voltage-dependent, linear reduction of the permissible current of Imax, starting at a supply voltage U=12.2V up to a reduced motor current limit Imax, red at a supply voltage U=9V. Applying these motor current limit values then results in exemplary switching voltages of 11.8V, 10V, and 9.2V; see Fig. 9b.
[0080] Fig. 10 illustrates another optional design variant: The voltage ranges most frequently encountered in vehicles, for example, from 12V to 13.5V, can be operated without speed jumps by specifying suitable motor current / current limit / setpoint speed combinations. Accordingly, the electric motor must be designed so that it can deliver the maximum expected torque down to a supply voltage of 11.5V without exceeding the motor current / current limit. Furthermore, for acoustic reasons, it may be advantageous not to approach the maximum current limit at operating voltages above, for example, 13.5V, and thus not to increase the speed accordingly, but to pursue a constant speed strategy:
[0081] Fig. 10 illustrates various operating ranges. In ranges 5a to 5, the compressor module 10 is operated according to the "constant speed" strategy. The target speed is identical to the speed in the preferred voltage range 5 to 5b. In ranges 5 to 5d, the compressor module 10 is operated according to the "target current limitation" strategy. The parameterized target speeds prevent a speed jump within the most frequently occurring voltage ranges (5b to 5).
[0082] Reference symbol (part of the description)
[0083] 10 Compressor module
[0084] 12 Compressor
[0085] 14 Electric motor
[0086] 14.1 Stator
[0087] 14.2. Rotor
[0088] 14.3 Stator coil
[0089] 14.4. Hall sensor
[0090] 16 Engine electronics
[0091] 18 air dryers
[0092] 20 air distributors
[0093] 30 Compressed air supply system
[0094] 32 air suspension system
[0095] 34 air springs
[0096] 36 compressed air reservoir
[0097] 38 air dryers
[0098] 40 Main pressure line
[0099] 42.2 One-way valve / check valve
[0100] 50 2 / 2-way valve
[0101] 42 Return spring (of the 2 / 2-way valve 50)
[0102] 44 Control solenoid (of the 2 / 2-way valve 50)
[0103] 56 vent valve
[0104] 60 3 / 2-way valve
[0105] 52 Return spring (of the 3 / 2-way valve 60)
[0106] 54 control pistons (of the 3 / 2-way valve 60)
[0107] 70.1 , 70.2 Throttle
[0108] 100 control unit
[0109] 102 Current sensor
[0110] 104 analog-to-digital converters
[0111] 106 Interface
Claims
Patent claims 1. Compressor module (10), in particular for a compressed air supply system (20) of a vehicle, wherein the compressor module (10) comprises a compressor (12) and a speed-controlled, preferably brushless electric motor (14) for driving the compressor (12), during the operation of which a motor current (IB) occurs and to which motor electronics (16) with an electronic commutator and speed control are assigned, characterized in that the compressor module (10) is connected to or comprises an electronic control unit (100), wherein the electronic control unit (100) is designed to predetermine one of at least two different target speeds for the electric motor (14) as a function of the average motor current (IB), namely at least one predefined first target speed (m , son) and a predefined second target speed (n2, son) which is lower than the predefined first target speed (m , son),and to switch from specifying the predefined first target speed (m . soii) to specifying the predefined second target speed (n2, son) when the average motor current (IB) reaches or exceeds a predetermined motor current limit value (Imax; Imax, red).
2. Compressor module (10) according to claim 1, for which more than two target speeds are specified, wherein the control unit (100) is designed to be dependent in each case on the specification of a predefined higher target speed (n x , son) to specify the predefined lower target speed (nx+i son,) when the average motor current (IB) reaches or exceeds the specified motor current limit value (Imax; Imax, red).
3. Compressor module (10) according to claim 1 or 2, which can be supplied with at least two supply voltages (Uv) of different levels, wherein the control unit (100) is designed to specify predefined motor current limit values (Imax; Imax, red) for the at least two different supply voltages (Uv), wherein the motor current limit values (Imax; Imax, red) predefined for the at least two different supply voltages (Uv) are different from one another.
4. Compressor module (10) according to claim 3, wherein the control unit (100) is designed to apply reduced motor current limit values (I max, red ) for supply voltages (Uv) whose respective voltage values are below a limit voltage value (Uv limit), which are lower than a predefined maximum motor current limit value (Imax).
5. Compressor module (10) according to at least one of claims 1 to 4, wherein the maximum motor current limit value (I max) is adjustable to one of at least two different, predefined maximum motor current limit values (Imax, Imax, red).
6. Compressor module (10) according to at least one of claims 1 to 5, wherein the electric motor (14) comprises an electrically commutable stator (14.1), a permanently excited rotor (14.2), and the motor electronics (16) which forms at least one speed-controlled electronic commutator which generates an electric rotating field for the electric motor (14) according to a predetermined target speed (n S oii) is generated.
7. Compressor module (10) according to at least one of claims 1 to 6, which has at least one current sensor (102) for detecting the current (IB) consumed by the electric motor (14), an analog-digital converter (104) for converting an output value supplied by the current sensor (102) and representing the current (IB) consumed by the electric motor (14) into a digital signal representing the current (IB) consumed by the electric motor (14), and an interface (106) via which the digital signal representing the current consumed by the electric motor (14) can be called up during operation.
8. Compressor module (10) according to at least one of claims 1 to 6, wherein the electric motor (14) is designed such that the electric motor (14) can deliver a maximum expected torque down to a supply voltage of 11.5V without the motor current limit value (Imax, Imax, red) being exceeded.
9. Compressed air supply system (30) for a motor vehicle with a compressor module (10) according to one of claims 1 to 8, at least one compressed air consumer (34), in particular an air spring system (32) or a brake system, controllable valves (50) and a compressed air control unit (36) for controlling the valves (50).
10. Compressed air supply system (30) according to claim 9, which has a compressed air reservoir (36) and which is switchable between an open operation and a closed operation. 1 . A method for operating a compressed air supply system (30) with a compressor (12) and a speed-controlled electric motor (12) for driving the compressor (12), the method comprising the steps of: Specifying a predefined first target speed (m son), regularly or continuously comparing a current value of the average motor current (IB) consumed by the electric motor (14) during operation with a predefined maximum motor current limit value (Imax; Imax. red) Specifying a predefined second target speed (n2 son) which is lower than the predefined first target speed (m son) as soon as a current value of the average motor current (IB) is greater than or equal to the predefined maximum motor current limit value (Imax).