Patent Publication Number: US-2022234409-A1

Title: Air spring control system, air spring system, vehicle including same, and method for same

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of international patent application PCT/EP2020/081467, filed Nov. 9, 2020 designating the United States and claiming priority from German application 10 2019 130 087.8, filed Nov. 7, 2019, and the entire content of both applications is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The disclosure relates to an air suspension control system for a vehicle. The disclosure relates additionally to an air suspension system which is controllable via an air suspension control system, to a vehicle having such an air suspension system and/or air suspension control system, and to a method for operating such a vehicle. 
     BACKGROUND 
     The vehicle can be a commercial vehicle, such as, for example, a bus, a truck or a truck-trailer combination, or a passenger vehicle. Air suspension control systems are also referred to as ECAS (electronically controlled air suspension). 
     Air suspension systems for vehicles are known which improve ride comfort and safety by the use of air springs. This is achieved, for example, by protecting the structure and occupants of a vehicle via the air springs against jolts caused by unevenness of the ground when the vehicle is moving. In addition, vibrations caused by unevenness of the ground when the vehicle is moving can be damped or even prevented. 
     In the case of air suspension systems, a distinction is further to be made between adjustable and non-adjustable suspension systems. Adjustable air suspension systems usually have a variable gas mass, preferably air mass, of the air springs, while the gas mass of the air springs is fixed in the case of non-adjustable air suspension systems. Non-adjustable air springs can be used primarily for the above-mentioned purposes, while adjustable air springs permit enhanced functions. Such an enhanced function of an adjustable air suspension system is, for example, level control, in which an adjustment of the ride height of a vehicle, for example in dependence on a vehicle load, is kept constant. 
     In order to achieve further functions, adjustable or variable air suspension systems have an air suspension control system which varies the gas mass in a spring element in dependence on sensors, for example. Manual intervention with control signals, as is known, for example, in the case of an automatic lowering system in a bus for facilitating the entry and exit of passengers, is also known. 
     In the present case, consideration is to be given to an adjustable air suspension system in which a variable gas mass is used in air springs, in particular for the suspension of a vehicle. In this case, not all the axles of the vehicle are necessarily sprung via the air suspension, but rather one or more axles of the vehicle can be steel-sprung. 
     As already mentioned above, such air suspension systems generally have an air suspension control system which is connected to a plurality of sensors and actuators for controlling the gas mass of the air springs. A plurality of measured values is thus supplied to an air suspension control system, which is usually part of a control device including further functions. In addition, the control device must transmit a plurality of commands far actuating the actuators. Moreover, the control device must have a quick response time in order to generate corresponding control signals from the plurality of measured values. 
     A control device which the air suspension control system includes is therefore subject to a highly complex development effort and requires a very high computing capacity. In particular, the air suspension system as a whole is shut down in the event of failure of the control device. 
     Non-prepublished German patent application DE 10 2018 111 003.0 (corresponding to US 2021/0245567) of the applicant discloses an air suspension control system (ELAS) for a commercial vehicle or a passenger vehicle. The air suspension control system has a main control unit for operating the air suspension control system. In addition, the air suspension control system includes at least two auxiliary control units. The auxiliary control units are each connected to the main control unit via a data link. The data link is either a shared data link or a separate data link. That is, in the case of a shared data link, the main control unit and the two auxiliary control units are connected to a shared data line, for example including two or more electrical conductors. If the data link is in the form of a separate data link, this means that a separate data line is provided between the main control unit and each of the at least two auxiliary control units. 
     Each of the auxiliary control units has at least one output. The output serves to actuate at least one actuator which can be connected to the output. An actuator is, for example, an adjustment drive for a valve. Preferably, the actuator is an electromagnetic valve component, which is, for example, a pneumatic or hydraulic valve component. Particularly preferably, the valve is a solenoid valve. 
     At least one function for generating control signals at the output can be stored in each of the auxiliary control units. That is, the auxiliary control unit is preferably adapted to actuate an output in dependence on a stored function which is stored in the auxiliary control unit. 
     The main control unit is additionally adapted to call up and/or parameterize the stored function. This is effected by the transmission of commands via the data link from the main control unit to the auxiliary control unit whose function is to be called up and/or parameterized. 
     Calling up is to be understood here and in the following as meaning in particular that, by calling up a function, the auxiliary control unit is brought into operation with that function and control signals are subsequently generated at the output of the auxiliary control unit in dependence on the called-up function. 
     Here and in the following, the term function is not limited to a mathematical function in the sense of a representation of a relationship between two quantities. Rather, the term function is also to be understood in the present case in its meaning as used in computer science. 
     Accordingly, a function is a program construct which without input values, or preferably with input values, for example including input data and/or sensor data and/or a parameterization, generates output values. 
     Compared to conventional air suspension control systems which have only a single control unit with which all the actuators are actuated via their outputs, the control unit according to DE 10 2018 111 003.0 is thus of modular construction. The main control unit serves substantially only to call up and/or parameterize the functions stored in the auxiliary control units. 
     A stored function can be, for example, a level control function. Accordingly, the level control function is called up by the main control unit in the auxiliary control units as required. The parameter specified by the main control unit to the auxiliary control units can be, for example, a desired ride height which is to be kept constant. When the level control function is called up, valves are then actuated in the auxiliary control unite such that gas masses are guided into or out of the air springs in order to keep the specified ride height substantially constant. 
     If remaining with the above example of the level control function level control of one or more air springs is to be carried out by all the auxiliary control units, the main control unit can, for example, call up the corresponding function or level control function in a single call to all the auxiliary control units. After calling up the level control function, the main control unit no longer has to interact for this purpose. 
     A modular construction of the air suspension control system is thereby possible, so that, for example, the same main control unit can always be used in the vehicle irrespective of the number of necessary auxiliary control units. In addition, data traffic on the data link(s) can be greatly reduced or even avoided completely once a function has been called up. 
     The bandwidth of a data link can thus be used for other communications. 
     In addition, a lower computing capacity of the main control unit is also necessary, since the functions are relocated into the auxiliary control units. A main control unit, with the same computing capacity, can thus perform other functions and can be limited, in terms of an air suspension, substantially to superordinate monitoring functions of the air suspension without having to carry out a time-critical control of the air suspension. 
     SUMMARY 
     Accordingly, it is an object of the disclosure to provide an air suspension control system which provides enhanced functions with a lower structural outlay. 
     The disclosure uses the modular construction of the air suspension control system having a main control unit and auxiliary control units according to DE 10 2018 111 003.0 in a particular way: According to the disclosure, it has been recognized that, for the particular case of a vehicle with an air-sprung first axle and a second axle which does not necessarily have to be air-sprung, the at least two auxiliary control units according to DE 10 2018 111 003.0 are not necessary, but rather complete functionality can be achieved with an even simpler air suspension control system. 
     The air suspension control system is provided for a vehicle with a first axle and a second axle. The air suspension control system has a main control unit for operating the air suspension control system and an auxiliary control unit which is connected to the main control unit via a data link. The auxiliary control unit has a pressure sensor associated with the first axle of the vehicle for determining pressure measurements of the first axle. The pressure measurements are processed as pressure sensor signals. The pressure sensor can be integrated in the auxiliary control unit. 
     The auxiliary control unit additionally has an input for acquiring height sensor signals. A first height sensor arranged on the first axle of the vehicle and a second height sensor arranged on the second axle of the vehicle can be connected to the input. First height measurements can be received as first height sensor signals by the first height sensor arranged on the first axle of the vehicle. Second height measurements can be received as second height sensor signals by the second height sensor arranged on the second axle of the vehicle. 
     The auxiliary control unit is adapted to transmit the first and/or second height sensor signals and/or the pressure sensor signals to the main control unit via the data link. The main control unit is adapted to carry out on-board weighing for the first axle and/or the second axle in dependence on the first and/or second height sensor signals and/or the pressure sensor signals. 
     The first and second height sensor signals and the pressure sensor signals are combined together as “sensor signals” in the following. Thus, when on-board weighing or a function is carried out in dependence on a sensor signal, the on-board weighing or the function can be carried out in dependence on a first height sensor signal, on a second height sensor signal and/or on a pressure signal or on any desired combinations thereof. 
     Vehicles which have a first axle and a second axle can but do not have to be two-axle vehicles. Vehicles which have a first and a second axle can have a driven axle, which can be a rear axle. The driven axle can be air-sprung. The further of the two axles, which can correspondingly be a front axle, can likewise be air-sprung. However, the further of the two axles can also be steel-sprung. In particular in the case where the further axle is steel-sprung, it is not necessary for operation of the air suspension control system that an auxiliary control unit is arranged on the further axle, since no air-suspension bellows and no actuators which can be actuated to admit air to and remove air from the air-suspension bellows are arranged on a steel-sprung axle. Steel springs do not have to be actuated during operation. In this case, an air suspension control system according to DE 10 2018 111 003.0 having at least two auxiliary control units that is, here an auxiliary control unit for each of the two axles would be unnecessarily complex, elaborate and expensive, and also more susceptible to faults owing to the use of increased electronics by the two auxiliary control units. The disclosure can thus be used in particular in vehicles in which it is not necessary to use more than only one auxiliary control unit for operating an air suspension. 
     Indeed, it can be also desirable in the case of such a vehicle, in which more than one auxiliary control unit is not necessary for controlling the air suspension, to utilize additional functionalities of the air suspension control system which go beyond immediate air suspension control. These can include, for example, on-board weighing, in which a load of the vehicle is determined directly on the loaded vehicle. On-board weighing can be used, for example, in vehicles which are frequently unloaded and loaded during operation, in order to ensure that such vehicles on the one hand transport as large a load as possible, in order to be efficient, but on the other hand are also not overloaded, which could lead on the one hand to increased wear and on the other hand to immediate danger. On-board weighing can, however, also be used, for example, in the case of the purchase or sale of bulk material, in order to be able to determine an added quantity of the bulk material particularly easily, in order to determine a total price. For on-board weighing, a height sensor is to be provided on each axle at which the axle load is to be determined, in order to determine a deflection at that axle if it is a steel-sprung axle. If it is an air-sprung axle, a pressure sensor is to be provided, in order to determine a bellows pressure in air-suspension bellows on that axle. 
     The main control unit can calculate an axle load for the axle in question from the deflection or the bellows pressure and an axle load characteristic curve stored in the main control unit. For calculation of an axle load, reference is made to patent applications DE 10 2018 128 233.8 and DE 10 2019 111 187.0 of the applicant, in which examples of methods for determining an axle load of an air-sprung axle or of a steel-sprung axle are described. 
     The pressure sensor and/or the height sensors can also be used for other functions in the vehicle. For example, the pressure sensor can also be used for pressure ratio control between drive axles and trailing and/or lift axles. In the case of an air-sprung axle, an associated height sensor can also be used for determining a distance between the chassis and the axle. 
     According to an embodiment of the disclosure, the input of the auxiliary control unit can be connected to a further sensor in order to receive further sensor signals. The further sensor can be, for example, a sensor for detecting distances between the axles and the wheel housings, for example, or a distance of a floor of the vehicle from the ground. 
     Alternatively or cumulatively, it is also possible that the auxiliary control unit, in order to receive further sensor signals of the further sensor or of a further sensor, has a further input which can be connected to the further sensor in order to receive the further sensor signals. 
     According to an embodiment of the disclosure, the auxiliary control unit can have an output for actuating an actuator which can be connected to the output. A function for generating control signals at the output can then be able to be stored in the auxiliary control unit, and the main control unit can be adapted to call up and/or parameterize at least the stored function by transmitting commands via the data link. The auxiliary control unit can then be adapted to generate control signals at the output in dependence on the first and/or second height sensor signals and/or the pressure sensor signals, Preferably, the auxiliary control unit is adapted to generate control signals at the output in dependence on the sensor signals and a function, in particular a stored, called-up function. Accordingly, values of sensor signals or values derived therefrom are particularly preferably so linked with a function that is carried out in the auxiliary control unit that specific control signals are generated at the output. 
     In the case of the above-mentioned level control function, a current state of the prevailing ride height, for example, determined via one of the height sensors or via both height sensors, is supplied to the auxiliary control unit as sensor data, so that an actuator for changing the ride height or for maintaining the ride height can correspondingly be actuated at the output. Complete control of a single closed system is thus possible with an auxiliary control unit when, for example, sensor data are considered as the actual value, the function has target value specifications and control takes place via the output by actuation of one or more actuators. 
     A single, self-contained control system including the auxiliary control unit can accordingly carry out control in an autonomous manner, separately from and independently of the main control unit, once it has been activated by the calling up of a function by the main control unit. The above-mentioned parameterization of the function can represent, for example, a target value specification for the function. 
     In particular for adjusting an actuator for varying or keeping constant a ride height via an auxiliary control unit, complete controllability by the auxiliary control unit without further instructions by a main control unit is possible by acquiring distances, for example, between the axles and the wheel housings or between the distance of the floor of the vehicle from the ground and/or by recording pressure measurements with a pressure sensor in order to evaluate a loading situation. 
     According to an embodiment of the disclosure, the auxiliary control unit is adapted to receive and interpret at least one predefined fixed set of commands from the main control unit. The auxiliary control unit can also be adapted to store a predefined fixed set of functions in the auxiliary control unit. Accordingly, the main control unit, for example, is configured with a fixed set of commands, wherein the interpretation of a command takes place in dependence on the configuration of a function stored in the auxiliary control unit. 
     An individual adaptation of the air suspension control system can accordingly take place solely by adaptation of the auxiliary control unit, Thus, the main control unit can always be identical, irrespective of the individual construction of a vehicle or the requirements of the vehicle in which an air suspension control system is to be used. The same main control unit can accordingly be used, for example, for a plurality of different individual vehicles, so that it is possible to produce the main control unit less expensively because of the large quantities that are required. 
     According to a further embodiment, the auxiliary control unit is also adapted to transmit sensor signals to the main control unit via the data link when a command is sent by the main control unit via the data link and this command is received by the auxiliary control unit. The command can be, for example, that a sensor signal is to be read. Preferably, the main control unit can accordingly be used as a monitoring body, for example for a correct function, even if control using sensors and actuators is itself carried out within the auxiliary control unit. The main control unit is, for example, so configured that, at intervals or when triggered by a request from a further superordinate body, it checks, on the basis of sensor signals or other data of the auxiliary control unit, that the auxiliary control unit is operating correctly and/or without error. 
     The auxiliary control unit can be arranged on the first axle of the vehicle, wherein in particular the first axle of the vehicle is air-sprung. The second axle of the vehicle can be steel-sprung. The vehicle can be a two-axle vehicle, that is, have exactly the first axle and the second axle. The first axle can be a rear axle of the vehicle, so that the rear axle of the vehicle can be an air-sprung axle and/or the rear axle of the vehicle can have the pressure sensor. The pressure sensor is preferably associated with the air-sprung axle. The second axle can be a front axle of the vehicle, so that the front axle of the vehicle can be a steel-sprung axle or also an air-sprung axle and/or the front axle of the vehicle can have only a height sensor and no pressure sensor or auxiliary control unit. 
     According to an embodiment of the disclosure, the data link is a bus link. In particular, the bus link is a CAN bus link. A main control unit can thus be arranged, for example, in the region of the vehicle in which further superordinate control units are present, while the auxiliary control unit can be arranged, for example, in the region close to one or more actuators that are to be controlled. A data link in the form of a bus link, in particular in the form of a CAN bus link, is particularly advantageous for connecting the main control unit to the auxiliary control unit since a bus link is already planned or present in today&#39;s vehicles. A bus link that is already present can be used to achieve communication between the auxiliary control unit and the main control unit without additional cable connections having to be provided. 
     The disclosure relates additionally to an air suspension system which in particular has an air suspension control system as described hereinbefore and/or which in particular is controllable via an air suspension control system as described hereinbefore. The air suspension system has a first height sensor arranged on the first axle of the vehicle and connected to the input of the auxiliary control unit for determining first height measurements and a second height sensor arranged on the second axle of the vehicle and connected to the input of the auxiliary control unit for determining second height measurements. 
     According to an embodiment of the disclosure, the air suspension system has an actuator for connection to the air suspension control system. The actuator is a valve drive and is adapted to actuate the flow through the valve opening, connected to the valve drive for actuation, of a valve in a continuous manner or in more than three steps. 
     It is thereby possible, for example, to adjust the speed with which the ride height is varied. For example, the ride height can thus be changed at a lower speed when the vehicle is moving than when it is stationary in order, for example, not to exert an abrupt influence on the driving dynamics while the vehicle is moving. 
     In particular in the case of buses, this has the advantage that the ride height can be adjusted particularly quickly when the bus is stopped for the entry and exit of passengers. This is preferably possible via the same valve that assists with level control while the vehicle is moving, without the need for multiple valves connected in parallel. 
     According to one embodiment, the valve drive has a stepper motor. A stepper motor is adjustable in a simple manner in a plurality of steps, so that, depending on the step size of the stepper motor used, a plurality of steps is possible for actuating the valve. According to one embodiment, the actuator of the air suspension system is configured to be connected to an output of the auxiliary control unit. 
     The disclosure relates additionally to a vehicle with a first axle and a second axle, which in particular is a commercial vehicle or a passenger vehicle and has an air suspension control system as described hereinbefore and/or an air suspension system as described hereinbefore. 
     The disclosure relates additionally to a method for operating such a vehicle having an air suspension control system as described hereinbefore and/or an air suspension system as described hereinbefore. 
     According to an embodiment of the method, control signals are generated at the output of the auxiliary control unit in dependence on functions which are stored in the auxiliary control unit and in dependence on commands which are sent by a main control unit to the auxiliary control unit. 
     It is possible that the control signals are additionally generated in dependence on sensor signals of at least one sensor connected to the auxiliary control unit. According to an embodiment of the disclosure, control signals are generated at the output of the auxiliary control unit in dependence on the first and/or second height sensor signals at the input and/or in dependence on the pressure sensor signals. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described with reference to the drawings wherein: 
         FIG. 1  shows a schematic diagram of an air suspension control system and of an air suspension system having two auxiliary control units in the case of two air-sprung axles; 
         FIG. 2  shows a schematic diagram of an air suspension control system and of an air suspension system having two auxiliary control units in the case of an air-sprung axle and a steel-sprung axle; 
         FIG. 3  shows a schematic diagram of an air suspension control system and of an air suspension system having one auxiliary control unit in the case of an air-sprung axle and a steel-sprung axle; and, 
         FIG. 4  shows an air suspension system having an air suspension control system. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows an air suspension control system  10  and an air suspension system  26  for a vehicle  48 . The air suspension control system  10  includes a main control unit  12  and two auxiliary control units  14 . The auxiliary control units  14  are each connected to the main control unit  12  via a data link  16 . Accordingly, the data link  16  serves to transmit data from the main control unit  12  to the auxiliary control units  14  and from the auxiliary control units  14  to the main control unit  12 . 
     In  FIG. 1 , the data link  16  is represented by two individual lines, which each include, for example, a plurality of electrical or optical cables. According to another embodiment, which is not shown in  FIG. 1 , these two lines are not separate and there is a shared data link between the main control unit  12  and the two auxiliary control units  14  (see  FIG. 2 ). This shared data link is preferably a bus system. 
     Each of the auxiliary control units  14  has two outputs  18 , to each of which an actuator  20  is electrically connected. Each of the auxiliary control units  14  additionally includes two inputs  22 , to each of which a sensor  24  is connected. 
     The air suspension control system  10  is configured in such a manner that functions in the auxiliary control units  18  are first called up via the main control unit  12  via the data link  16  and are parameterized. On the basis of these functions, output signals are then generated at the outputs  18  for the actuators  20  in dependence on the function and also on sensor data which are provided via the sensors  24  to the inputs  22  of the auxiliary control units  14 . Functions are, for example, the raising or lowering of a vehicle with the air suspension control system or the tilting of the vehicle or level control during or after loading of a vehicle. 
       FIG. 2  shows an air suspension control system  10  and an air suspension system  26  corresponding to  FIG. 1 . The air suspension control system  10  likewise includes a main control unit  12  and two auxiliary control units  14 , wherein the auxiliary control units  14  are connected to the main control unit  12  via a data link  16 . In  FIG. 2 , the data link  16  is represented schematically as a single line, which includes, for example, a plurality of electrical or optical cables. The data link  16  can in this way form a shared data link  16  between the main control unit  12  and the two auxiliary control units  14 , for example in the form of a bus system. The data link can, however, also include two or more individual lines. 
     In contrast to  FIG. 1 , it is shown in  FIG. 2  that, of two axles  36  of the vehicle with wheels  38 , only one axle  36   a  is air-sprung and accordingly has air-suspension bellows  40  with actuators  20 . The other axle  36   b  is steel-sprung and accordingly has steel springs  42 . 
       FIG. 2  shows two different types of sensors  24 : On the one hand, a pressure sensor  46  is arranged in each of the auxiliary control units  14 . By associating an auxiliary control unit  14  with each of the axles  36 , a pressure sensor  46  is thus also associated with each of the axles  36 . 
     Furthermore, a height sensor  44  is associated with each of the axles  36 , wherein precisely one height sensor  44  is here associated with each of the auxiliary control units  14 , wherein the auxiliary control unit  14  and the height sensor  44  associated therewith are in each case associated with the same axle  36 . 
       FIG. 3  shows, in an analogous manner to  FIG. 2 , an air suspension control system  10  having a main control unit  12 . The air suspension control system  10  according to  FIG. 3  is likewise arranged on a vehicle which has an air-sprung axle  36   a  and a steel-sprung axle  36   b . According to  FIG. 3 , however, an auxiliary control unit  14  is arranged only on the air-sprung axle  36   a . Accordingly, a pressure sensor  44  is also associated only with the air-sprung axle  36   a . However, a height sensor  44  is associated with both the air-sprung axle  36   a  and the steel-sprung axle  36   b . The two height sensors  44  are associated with the same auxiliary control unit  14  arranged on the air-sprung axle  36   a . This is possible because the auxiliary control unit  14  has two inputs  22  for height sensor data. It is, however, also possible that the two height sensors  44  are connected to the same input  22  of the auxiliary control unit. 
     Because there is here only one air-sprung axle  36   a  at which air-suspension valves  38  must be actuated via the actuators  20 , one auxiliary control unit  14  is sufficient for fully controlling the air suspension of the vehicle. However, by associating the height sensor  44  of the steel-sprung axle  36   b  with the auxiliary control unit  14  in addition to the height sensor  44  of the air-sprung axle  36   a  and the pressure sensor  46  of the air-sprung axle  36   a , the auxiliary control unit  14  and the main control unit  12  can evaluate the sensor data of the sensors  24 ,  44 ,  46  such that additional functions that go beyond mere air suspension can be ensured: 
     A deflection of the air-sprung axle  36   a  and/or of the steel-sprung axle  36   b  can be determined from the height sensor data of the height sensor  44  of the air-sprung axle  36   a  and/or the height sensor data of the height sensor  44  of the steel-sprung axle  36   b . Determination of the deflection can be carried out by the main control unit  12  in that the height sensor data are transmitted by the auxiliary control unit  12  to the main control unit via the data link  16 . The pressure sensor data can also be transmitted by the auxiliary control unit  14  to the main control unit via the data link  16 . The main control unit  12  can carry out on-board weighing for the steel-sprung axle  36   b  on the basis of the deflection thereof and for the air-sprung axle on the basis of the pressure sensor data, which can indicate a bellows pressure in the air-suspension bellows  40 . 
       FIG. 4  shows an air suspension system  26  which is controllable via the air suspension control system  10 . The air suspension system here has an actuator  20  which is in the form of a valve drive  28 . The valve drive  28  is accordingly connected to an output  18  of the auxiliary control unit  14 . The valve drive  28  is part of a valve  30  and has a stepper motor  32  for actuating a valve opening  34  of the valve  30  in a continuous manner or in more than three steps. 
     The valve  30  is thus actuated by the auxiliary control unit  14  in such a manner that a step of the valve opening  34  which is desired is provided for the valve drive  28 . The valve drive  28  then adjusts the valve opening  34  according to the desired step via the stepper motor  32 . The flow through the valve  30  is thereby varied in such a manner that, for example, slow or rapid raising of a vehicle is made possible by filling a cylinder with gas, in particular air, according to the flow. 
     It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims. 
     LIST OF REFERENCE NUMERALS (PART OF THE DESCRIPTION) 
     
         
           10  air suspension control system 
           12  main control unit 
           14  auxiliary control unit 
           16  data link 
           18  output for connection of an actuator 
           20  actuator 
           22  input for acquisition of sensor data 
           24  sensor 
           26  air suspension system 
           28  valve drive 
           30  valve 
           32  stepper motor 
           34  valve opening 
           36  axle 
           38  wheel 
           40  air-suspension bellows 
           42  steel spring 
           44  height sensor 
           46  pressure sensor 
           48  vehicle