EP1656267A1

EP1656267A1 - Method for controlling the level of pneumatic level-control systems in motor vehicles

Info

Publication number: EP1656267A1
Application number: EP04729865A
Authority: EP
Inventors: Alexander Stiller
Original assignee: Continental AG
Current assignee: Continental Teves AG and Co OHG
Priority date: 2003-07-12
Filing date: 2004-04-28
Publication date: 2006-05-17
Also published as: WO2005005181A1; US7441782B2; US20070040344A1; DE10331600B4; DE10331600A1

Abstract

The invention relates to a method for controlling the level of a pneumatic level-control system of a motor vehicle comprising at least two axles, at least one pneumatic spring (2a, 2b) per axle, optionally one or more pressure accumulators (3), at least one pressure sensor (24), elements (16, 18, 20, 22) for determining the distance between at least one wheel and/or an axle and the vehicle body, a control unit (10) and a compressor (12). The axle levels are controlled in sequence and adjusted from a starting level to a target level. During a positive adjustment operation the compressor (12) is at least operated temporarily and/or a connection of at least one pneumatic spring (2a, 2b) to the pressure accumulator (3) is established. The positive adjustment operation for the pneumatic spring or springs (2a, 2b) on an axle from a starting level to a higher target level is interrupted by the control unit (10), if at least one shut-off condition of the compressor (12) has been fulfilled and/or the pressure level is too low in the pressure accumulator (3). To prevent the vehicle from leaning, after the interruption of the positive adjustment operation, the level in all axles is adjusted to a common intermediate level, which is closer to the target level than to the starting level.

Description

description

Level control method for pneumatic level control systems in motor vehicles

The invention relates to a method for level control of a pneumatic level control system of a motor vehicle with at least two axles, at least one air spring per axle, optionally one or more pressure accumulators, at least one pressure sensor, means for determining the distance between at least one wheel and / or an axle and the vehicle body , a control unit and a compressor. The axes are regulated one after the other from a start level to a target level. In the case of an adjustment process, the compressor is operated at least temporarily and / or at least one air spring is connected to the pressure accumulator. The control unit cancels the adjustment process of the air spring or the air springs on an axle from a start level to a higher target level if at least one shutdown condition of the compressor is met and / or the pressure level in the pressure accumulator is too low.

A method for level control of a pneumatic level control system of a motor vehicle of the type mentioned is known for example from DE 19621 946 C2. In this publication, an air suspension of a vehicle is described, which allows the level of the vehicle to be raised or lowered when stationary or to be kept at a predetermined level regardless of the load. A control unit which switches the compressor on and off comprises a computer which calculates an estimated value of an operating temperature of the compressor and switches it off when the estimated value exceeds an upper threshold value. The control unit or the computer switches the compressor on again when the estimated value falls below a lower threshold value. The last estimated value is increased when the compressor is switched on by a predetermined temperature jump, the measure of which depends on the amount of the estimated value depends. During compressor operation, the estimated value is increased by a positive gradient and, when the compressor is at a standstill, decreased by a negative gradient.

From DE 43 33 591 AI a motor control is known which switches off the motor or the driven compressor for a predeterminable time on the basis of a total switch-on time and thus protects the motor / compressor from overheating.

From DE 4030475 AI a method for controlling an engine is known in which the rising or falling temperature characteristic of the engine during

Operation or standstill is assumed. In the method, an instantaneous value for the temperature of the motor is estimated by monitoring the operating time or the duration of the standstill of the motor. If the estimated instantaneous value exceeds a predeterminable value, the operation of the motor is stopped and an alarm signal is output.

Methods for level control of level control systems for motor vehicles are known from the prior art, with which the temperature of an engine or a compressor can be estimated during operation without exceeding a predetermined limit value. The compressor can thus be safely protected against overheating. It is also known to fill an air spring from a pressure accumulator with compressed air and thus to increase the level of the vehicle. It can happen that the pressure level in the pressure accumulator is not sufficient to fill the air spring with the required air volume, which is necessary for the desired level to be set. This is the case, for example, when the pressure level in the pressure accumulator is equal to or approximately the same as the pressure level of the air spring and there is no longer any air exchange between the pressure accumulator and the air spring. It is known from the prior art to combine the regulation methods with the compressor and pressure accumulator, so that the pressure level in the pressure accumulator can be increased again by the compressor. The methods described above have the disadvantage that an adjustment process is terminated to a predetermined target level when the limit or threshold value is reached. Since the axles of a vehicle are normally regulated one after the other from the starting level to the target level, it can happen that one or, in particular, trucks have already reached the target level, with the axis to be controlled no longer reaching the target level due to the triggering of the switch-off condition, which results in the vehicle being skewed. In order to compensate for the skew, it is known from the prior art to downgrade all axes to the starting level.

So that the motor vehicle is not at an angle, it is known from the prior art to lower the level on all axles to the starting level, so that the original level is set again as before the start of the regulating process. As long as the compressor operation is switched off, the compressor can cool down, which may take a long time. The adjustment process is restarted either automatically or based on a driver's request (pressing a button) if a switch-on condition of the compressor is fulfilled. In unfavorable cases, for example in extreme environmental conditions, it may happen that the cooling of the compressor due to the switch-on condition is not sufficient to regulate the motor vehicle from the start level to the target level, and a further up-setting process is interrupted again by the switch-off condition.

The object of the invention is to provide a method for level control of level control systems for motor vehicles, by means of which the energy consumption is reduced and the switching frequency of the corresponding components is reduced and the desired target level can be reliably achieved even under extreme environmental conditions.

This object is achieved by the characterizing features of claim 1. The level on all axles of the motor vehicle is regulated to a common intermediate level, which is closer to the target level than the starting level. Either a temperature limit value, a time limit value or a current limit value can be defined as the shutdown condition of the compressor. If a temperature limit is set as a switch-off condition, the temperature of the compressor can be measured directly on the compressor or in the vicinity of the compressor using a temperature sensor. Otherwise, the temperature can be estimated using methods such as are known, for example, from DE 19621 946 C2, DE 43 33 591 AI or DE 40 30475 AI. Alternatively, a time limit can be monitored as a shutdown condition. In this case, the control unit monitors the switch-on time of the compressor, for example by means of a counter. Or a current limit value of the compressor motor is defined as a switch-off condition, which is determined by the control device, for example by means of a signal from a current measuring coil.

The adjustment process of an air spring from the pressure accumulator can be interrupted due to an insufficient pressure level in the pressure accumulator. This is the case if the pressure drop between the pressure accumulator and the corresponding air spring is too small to raise the level on the air spring. In this case, a threshold value for the pressure level in the pressure accumulator is preferably set in the control unit, for example, which detects the pressure drop in the pressure accumulator below this pressure threshold and makes it available for further processing.

If the shutdown condition of the compressor is triggered or the pressure level in the pressure accumulator falls below the pressure threshold during an adjustment process, then »the compressor operation is switched off or the connection between the air spring (s) and the pressure accumulator is interrupted and the level on all axles of the motor vehicle becomes regulated to the intermediate level, the intermediate level being higher than that

Start level. It is thus ensured that the level of the motor vehicle increases compared to the starting level if the upward adjustment process of the last axle to be adjusted (in the case of cars, this is generally the rear axle upward adjustment) has been carried out at least in part. This means that the desired target level can be achieved even under extreme environmental conditions, since at least a small increase in the intermediate level compared to the starting level is always carried out. Another advantage of The invention is that the switch-on frequency and the switch-on time of the compressor, including the motor and the corresponding valves, can be reduced, since a renewed adjustment process only needs to take place from the intermediate level to the target level. The shorter running time of the compressor saves energy.

According to a development of the invention according to claim 2, provision is made for the intermediate level to be determined on this axis after the termination of the raising process on an axis and before the start of the regulating process. The common intermediate height level is determined on the basis of data from the individual air springs, which are present when or after the termination of the upward adjustment process. As

Air spring-specific data include, for example, the current pressure in the air springs, the air spring volume and the current level height at the vehicle corner or axis of the corresponding air spring. The advantage of the development of the invention can be seen in the fact that the intermediate level can be controlled and regulated in a targeted manner, which shortens the control time and prevents unnecessary switching processes of the cross-blocking valves.

According to a development of the invention according to claim 3, it is provided that the intermediate level corresponds to the smallest actual level of one of the axles of the motor vehicle. If the switch-off condition of the compressor is triggered during an opening process and the compressor operation is switched off, the level of all axes of the

Motor vehicle lowered to the smallest actual level of one of the axles. The advantage of the development of the invention can be seen in the fact that the smallest actual level of all axes can be determined in a simple manner, in particular by evaluating the height signals of the height sensors by the control unit.

According to a development of the invention according to claim 4, it is provided that the intermediate level is set on the basis of an air exchange between the corresponding air springs of the respective axles of the motor vehicle without releasing air from the corresponding air springs of the level control system into the environment. The advantage of the development of the invention can be seen in the fact that no compressed air is generated unnecessarily and thus energy is saved. Located in the individual air springs of the respective axles before a different pressure level, then it is advantageous that the level of the axle with the highest pressure in the air springs is increased first. With more than two axles of the motor vehicle, the sequence is to be continued accordingly as soon as the respective axle has reached the desired level. In general, as a prerequisite for this development, it can be stated that both the pressure level and the height level on one axis or in the air springs of this axis are greater than or equal to the pressure level and height level of the other axis (s) or the air springs of this axis (n ) must be (p _t > p ₂ and hi> h ₂ ) in order to enable air exchange and, accordingly, height compensation between them.

If the adjustment process on one axle is now interrupted due to the shutdown condition of the compressor and / or the pressure level in the pressure accumulator is too low, then the air from the air springs of the already regulated axle (s) with the higher pressure can only partially reach the air springs or axis (s) that have not yet been adjusted to the target level so that all axes reach the same level. This process is regulated by the control unit. The control unit opens the solenoid valves of the corresponding air springs only briefly at a time, so that air can flow from one air spring with the higher pressure into the air spring with the lower pressure. There are short pauses between the common opening phases of the corresponding valves

To enable pressure equalization and the determination of the respective pressure in the air springs and the level of the individual axes.

According to a further development of the invention according to claim 5, it is provided that the raising process of an air spring or the air springs on the axles which has been interrupted according to claim 1 is automatically continued to the target level if a switch-on condition of the compressor is fulfilled, the intermediate level corresponding to the starting level according to claim 1 , The desired level request is saved in the control unit. The desired setpoint level is available in the control unit even after the compressor shutdown condition has been triggered, the up-regulation process has been terminated and the corresponding axes have been terminated. The advantage The development of the invention is that the Aufauf process continues to the target level as soon as the switch-on condition of the compressor is met. The target level is thus reached as quickly as possible without unnecessary loss of time. If the upward adjustment process of a vehicle axle from the pressure accumulator has been interrupted due to a too low pressure level, then the upward adjustment operation on the axle is preferably continued by the compressor as soon as the switch-on condition for it is fulfilled. Only then is the pressure level of the pressure accumulator increased as necessary.

According to a development of the invention according to claim 6 it is provided that the shutdown condition of the compressor is an upper limit temperature. The limit temperature can either be measured directly and determined using known estimation methods. The advantage of the development of the invention is to be seen in the fact that the upper limit temperature allows a simple and direct relationship to possible component damage to the compressor.

According to a development of the invention according to claim 7, it is provided that the upper limit temperature is determined directly at the compressor or in the vicinity of the compressor. The advantage of the development of the invention can be seen in the fact that the determination of the upper limit temperature at the compressor or in the vicinity of the compressor allows a simple and direct relationship to possible component damage to the compressor.

According to a development of the invention according to claim 8, it is provided that the switch-on condition of the compressor is a lower limit temperature. The advantage of the development of the invention is that the determination of the lower limit temperature allows a simple and direct relationship to the cooling properties of the compressor. The determination of a lower limit temperature at a certain point correlates with the critical component temperatures of the compressor in that the compressor can be switched on again without being damaged until the upper limit temperature is reached. According to a development of the invention according to claim 9 it is provided that the lower limit temperature is determined directly at the compressor or in the vicinity of the compressor. The advantage of the development of the invention is that the determination of the lower limit temperature allows a simple and direct relationship to the cooling properties of the compressor. The determination of a lower limit temperature at a specific point on the compressor or in the vicinity of the compressor correlates with the critical component temperatures of the compressor in that the compressor can be switched on again without being damaged until the upper limit temperature is reached.

According to a development of the invention according to claim 10, it is provided that the switch-off condition is a pressure threshold value for the pressure in the pressure accumulator. If the pressure level in the pressure accumulator falls below the pressure threshold value, then the switch-off condition is triggered and the upward adjustment process of the vehicle axle from the pressure accumulator is terminated. The advantage of the development of the invention can be seen in the fact that the pressure level in the pressure accumulator and thus the pressure threshold value can be determined without additional means and in a simple manner, for example by means of a pressure sensor or the like.

According to the invention according to claim 11, it is provided that in the control unit of the level control system a common intermediate height level of all axles or all air springs relative to the vehicle body is determined, which is closer to the target level than the starting level, and that the level on all axles or Air springs of the motor vehicle is regulated to the common intermediate level, so that the vehicle is no longer at an angle. It is therefore guaranteed that the level of the

Motor vehicle increased compared to the starting level when the Aufaufvorgang the last axis to be controlled has been carried out at least partially. This means that the desired target level can be achieved even under extreme environmental conditions, since at least a small increase in the intermediate level compared to the starting level is always carried out. Another advantage of the invention is that the switch-on frequency and the switch-on time of the compressor including the motor and the corresponding valves can be reduced, since a renewed adjustment process only needs to take place from the intermediate level to the target level. The shorter running time of the compressor saves energy.

According to a development of the invention according to claim 12 it is provided that the level control system carries out a method according to claims 2 to 10. The advantage of the development of the invention can be seen in the fact that the intermediate level can be controlled and regulated in a targeted manner, which shortens the control time and prevents unnecessary switching processes of the cross-blocking valves. The running time of the compressor is shortened and energy is saved.

According to a development of the invention according to claim 13 it is provided that a temperature sensor is arranged on the cylinder head of the compressor or outside or inside the compressor engine directly on the engine. The advantage of the development can be seen in the fact that the temperature sensor is placed directly on or in the vicinity of the heat-sensitive components of the compressor. This makes it easy to protect the components of the compressor against overheating and destruction. Another advantage of the development of the invention is that the temperature measured at the selected point creates a calculable relationship to all heat-sensitive components of the compressor. This means that all the heat-sensitive components of the compressor can be safely protected against overheating with a single temperature measuring point.

Exemplary embodiments and further advantages of the invention are explained in connection with the following figures, in which:

Fig. 1 shows schematically a level control system and

Fig. 2 shows the flow chart of a level control procedure.

Figure 1 shows a highly schematic representation of a level control system for a motor vehicle, only those necessary for the following explanations Components are shown. Such level control systems are known per se, so that they will only be briefly explained here. The level control system has air springs 2a, which are assigned to the front axle of the motor vehicle, and air springs 2b, which are assigned to the rear axle of the motor vehicle. A pneumatic vehicle body (not shown) of the motor vehicle is spring-mounted with the air springs 2a, 2b. The air springs 2a are connected via a cross line 4a and the air springs 2b are connected via a cross line 4b. Each cross line 4a, 4b contains two cross check valves 6a, 6b, one of which is assigned to an air spring 2a, 2b. In addition, the cross lines 4a, 4b are connected to a further line 8, via which the air springs 2a, 2b are filled with compressed air or via which compressed air is released from the air springs 2a, 2b. A pressure accumulator 3 is connected to the line 8 via a cross-blocking valve 5, so that the pressure accumulator 3 can be connected to the air springs 2a, 2b with the corresponding switching position of the cross-blocking valves 5, 6a, 6b or to the compressor 12 if the cross-blocking valve 5 is switched through accordingly.

To fill up the air springs 2a, 2b, the cross-blocking valves 6a, 6b are actuated by the control unit 10 of the level control system, so that they change from the great state shown in FIG. 1 to their other switching state and the cross lines 4a and 4b are "switched through" Compressor 12 is controlled by control unit 10 so that it delivers compressed air to air springs 2a, 2. To cancel the filling process, compressor 12 is stopped by control unit 10 and cross-blocking valves 6a, 6b are controlled by control unit 10 so that they 1, the pressure accumulator 3 can accordingly be filled with compressed air by the compressor 12 when the cross-blocking valve 5 is switched on, and when the cross-blocking valve 5 is switched on, the pressure in the pressure accumulator 3 can also be determined by a pressure sensor 24. The pressure signal is determined by the pressure sensor 24 to the control unit 10 for further vera processing (set pressure threshold).

In order to discharge compressed air from the air springs 2a, 2b, the cross-blocking valves 6a, 6b are actuated by the control unit 10, so that they are actuated by the one shown in FIG Change the grand state to the open switching state. In addition, the drain valve 14 is controlled by the control unit 10, so that it changes from the Grandzsutand shown in Figure 1 in the open switching state in which it connects the line 8 with the atmosphere. The air springs 2a, 2b are then connected to the atmosphere via the transverse blocking lines 4a, 4b and via line 8, so that air from them is discharged. In order to end or abort a drainage process, the cross-blocking valves 6a, 6b and the drainage valve 14 are closed by the control unit 10, so that they then return to the grand state shown in FIG.

Due to different axle loads and consequently different pressure in the air springs, the filling or draining takes place axle by axle.

By appropriate control of the cross check valves 6a, 6b and the drain valve 14, it is also possible to discharge compressed air from an air spring or from any combination of air springs (for example the air springs which are assigned to an axis). In order to discharge air from the air spring 2b, which is assigned to the wheel position “rear left”, for example the cross-blocking valve 6b assigned to this air spring 2b and the drain valve 14 must be transferred from the large state shown in FIG. 1 to the open switching state From the air spring 2b, which is assigned to the wheel position "rear right", the cross-blocking valve 6b assigned to this air spring 2b must also be transferred from the grand state shown in FIG. 1 to the other switching state.

In addition to the components mentioned so far, the level control system has height sensors 16, 18, 20 and 22, of which one air spring 2a, 2b is assigned to the level control system. With the help of the height sensor 16, the current level of the vehicle body in the area of the wheel position “front left” can be measured at any time with respect to a reference point. The same applies to the height sensors 18, 20 and 22. The current one measured by the height sensors 16, 18, 20 and 22 The level is transmitted by them to the control unit 10 of the level control system and evaluated there. Information about the current level of the vehicle body in the area of the wheel positions of the motor vehicle relative to a predetermined reference point is therefore available in the control unit 10 at all times. In addition, it can be determined in the control unit 10 which current level the vehicle body occupies on average with respect to an axis of the motor vehicle by averaging the measured values of the corresponding height sensors. If, for example, the level of the vehicle body with respect to the rear axle is to be determined, the measurement values are averaged in the control unit 10, which were transmitted from the height sensors 20 and 22 to the control unit 10.

The control unit 10 continuously checks whether the current level of the vehicle body in the area of a wheel position or the current level of the vehicle body with respect to an axis of the motor vehicle corresponds to a predetermined target level stored in the control unit 10 (the current level is the last one in the Control unit 10 understood on the basis of the measurement signals transmitted by the height sensors 16, 18, 20 and 22). If the current level is below the predetermined target level stored in the control unit 10, the control unit 10 initiates an upward adjustment process. For this purpose, the corresponding cross-blocking valves 6a, 6b and the compressor 12 or the cross-blocking valve 5 of the pressure accumulator 3 are switched. The regulating process is ended when the control unit 10 determines that the current level corresponds to the predetermined target level stored in the control unit 10. The control unit 10 then leads the corresponding cross-blocking valves 5, 6a, 6b back into the grand state shown in FIG. 1 and switches off the compressor 12 if necessary.

If the switch-off condition of the compressor 12 is met or the pressure threshold in the pressure accumulator 3 is reached or undershot before the setpoint level is reached, then the regulating process is stopped prematurely and the corresponding cross-blocking valves 5, 6a, 6b are switched back to the basic state shown in FIG. 1 and if necessary, the compressor 12 is switched off. As a shutdown condition of the compressor 12, a temperature of the is particularly simple Compressor 12, which can be determined with a temperature sensor 26. The temperature of the compressor 12 is continuously monitored by the control unit 10, so that when the shutdown condition occurs, the control unit 10 can immediately carry out the corresponding steps, such as shutting off the cross-blocking valves 6a, 6b and the compressor 12. How this happens in detail is explained in more detail in FIG. 2.

If the current level is above the predetermined target level stored in the control unit 10, the control unit 10 initiates a draining process. For this purpose, the corresponding cross check valves 6a, 6b and the drain valve 14 are switched, as already explained above. The draining process is ended when the control unit 10 determines that the current level corresponds to the predetermined level stored in the control unit 10. The control unit 10 then leads the corresponding cross-blocking valves 6a, 6b and the drain valve 14 back into the basic state shown in FIG.

The control unit 10 may also determine that the level of the vehicle body does not drop as expected during a deflation process because the motor vehicle is in a critical situation. In this case, the control unit 10 cancels the draining process.

The level control system optionally contains a pressure sensor 24 with which the air pressure in each individual air spring 2a, 2b and the pressure accumulator 3 of the level control system can be measured. To measure the air pressure in the air spring 2b, which is assigned to the wheel position “rear left”, the cross-blocking valve 6b assigned to this air spring 2b is converted from the great state shown in FIG. 1 by the control unit 10 to the other switching state, whereas all other cross-blocking valves 6a , 6b of the level control system remain in the great state shown in Figure 1. In this case, the static air pressure prevailing in the air spring 2b, which is assigned to the wheel position on the "rear left", is present at the drain sensor 24. The air pressure in the other air springs of the level control system can be measured accordingly. The respective measurement result of the pressure sensor 24 is transmitted to the control unit 10. The transmitted measurement result is assigned in the control unit 10 to the air spring 2a, 2b, whose cross-blocking valve 6a, 6b has activated it, and is evaluated and stored.

It is also possible to exchange air between the individual air springs 2a, 2b in order, for example, to compensate for an inclined position of the vehicle body. An air exchange is preferably carried out only between two air springs 2a, 2b at the same time. For this purpose, the respective cross-blocking valves 6a, 6b of the corresponding air springs 2a, 2b are simultaneously switched by the control unit 10 for a short time, so that air can flow from the air spring 2a, 2b with the higher level of pressure to the air spring 2a, 2b with the lower level of pressure. After the cross-blocking valves 6a, 6b have been closed, there is a short pause so that pressure equalization takes place and the pressure in the corresponding air springs 2a, 2b can be determined. The process can be repeated until the vehicle body is no longer skewed. A corresponding procedure can be used for an air exchange between the pressure accumulator 3 and an air spring 2a, 2b, in which case the cross-blocking valve 5 must be switched.

FIG. 2 describes the sequence of the control method in a control unit of a level control system of a motor vehicle with two axes. In a first step of the method, the state of the level control system is determined and stored in the form of the current level, the starting level N1. In a further step, the driver of the motor vehicle sets a new target level N2, for example by pressing a button, or the control unit itself, for example after aborting an opening process, which is higher than the starting level N1. Thereupon, the regulation of the first axle 1 of the motor vehicle is started from the starting level Nl to the target level N2. How the corresponding valves and the compressor are switched is explained in more detail in FIG. 1. During the regulation process, it is monitored whether a shutdown condition of the compressor or a drop below the pressure level in the drain accumulator (drain threshold pk) is met. The switch-off condition can be a temperature limit (Tk), a current limit or a time limit. If the switch-off condition is met during the opening process of axis 1, for example the temperature at or near the compressor is greater than or equal to a maximum limit temperature (TK> = Tmax) or the current pressure pa in the drain accumulator is less than or equal to the pressure threshold value pk (pa <= pk), then the adjustment process of axis 1 is interrupted. The regulation process of axis 1 to start level N1 is started. As soon as axis 1 has reached the start level, the regulating process of axis 1 is ended. The level control system thus returns to its state at the start of the leveling process of axis 1 with the starting level Nl.

If the switch-off condition is not met during the axis 1 adjustment process, for example the temperature at or near the compressor is less than a maximum limit temperature (TK <Tmax) or the current pressure pa in the drain accumulator is above the pressure threshold value pk (pa> pk), then the adjustment process of axis 1 is ended as soon as the target level N2 of axis 1 is reached. Then the process of raising axis 2 to setpoint level N2 is started. Here, too, a switch-off condition is determined during the opening process, which can be a switch-off condition of the compressor (so that the compressor is not irreparably damaged) or a drain threshold value in the pressure accumulator.

If the switch-off condition is met during the opening process of axis 2, for example the temperature at or near the compressor is greater than or equal to a maximum limit temperature (TK> = Tmax) or the current pressure pa in the drain accumulator is less than or equal to the drain threshold value pk (pa <= pk), then the upwarding process of axis 2 is canceled. The control unit uses the height signals of all height sensors to determine an intermediate level ZI, which corresponds, for example, to the current actual level of axis 2. The level on all axles of the motor vehicle is then lowered to this intermediate level ZI. For the example, this means that the level on axis 1 is lowered from the target level N2 to the intermediate level ZI. For this purpose, the downward adjustment process of axis 1 is started. The regulation process of axis 1 is ended as soon as the intermediate level ZI is reached. The level control system is set to a new start state, the new start level N1 corresponding to the intermediate level ZI.

However, the intermediate level can also be set by successively transferring air from the air springs with the higher pressure and the higher height level to the air springs with the lower pressure and the lower height level (as described in FIG. 1) until the vehicle body is balanced is. In this case, no air is released from the air springs into the environment. This process is not shown in Figure 2.

If the switch-off condition is not fulfilled during the upward adjustment process of axis 2, for example the temperature at or near the compressor is less than a maximum limit temperature (TK <Tmax) or the current pressure pa in the drain accumulator is greater than the drain threshold value pk (pa > pk), then the adjustment process of axis 2 is ended as soon as the target level N2 of axis 2 is reached. The level control system is then set to a new start state, the new start level N 1 corresponding to the target level N 2

LIST OF REFERENCE NUMBERS

(is part of the description)

2a Air spring front left (NL) or right (VR) 2b Air spring rear left (HL) or right (HR)

3 storage tanks

4a cross line

4b cross line

5 Cross check valve 6a Cross check valve Vome left or right

6b Rear cross valve on the left or right

8 line

10 control unit

12 compressor 14 drain valve

16 Vome left height sensor

18 Height sensor Vome right

20 Rear right height sensor

22 Rear left height sensor 24 Pressure sensor

26 temperature sensor

Claims

claims

1. Method for level control of a pneumatic level control system of a motor vehicle with at least two axles, at least one air spring (2a, 2b) per axle, possibly one or more drainage tanks (3), at least one pressure sensor (24), means for determining the distance between at least one Wheel and / or an axle and the vehicle body (16, 18, 20, 22), a control unit (10) and a compressor (12), the axles being regulated one after the other from a starting level to a desired level, with at least occasionally during an opening operation the compressor (12) is operated and / or a connection is made to at least one air spring (2a, 2b) to the pressure accumulator (3) and the regulating process of the air spring (2a, 2b) or the air springs (2, 2b) on an axis of a start level to a higher desired level is terminated by the control unit (10) if at least one shutdown condition of the compressor (12) is met and / or the drain level u in the drawer (3) is too low, characterized in that the level on all axles of the motor vehicle is regulated to a common intermediate level, which is closer to the target level than the starting level, so that the vehicle is no longer at an angle.

2. The method according to claim 1, characterized in that the intermediate level is determined after the termination of the control process and before the start of the control process to the common intermediate level.

3. The method according spoke 1 and / or claim 2, characterized in that the intermediate level corresponds to the smallest actual level of one of the axles of the motor vehicle.

4. The method according to one or more of the preceding claims, characterized in that the intermediate level is set on the basis of an air exchange between the corresponding air springs (2a, 2b) of the respective axles of the motor vehicle without releasing air from the corresponding air springs (2a, 2b) of the level control system into the environment.

5. The method according to one or more of the preceding claims, characterized in that the raising process of an air spring (2a, 2b) or the air springs (2a, 2b) on the axes, which has been interrupted according to claim 1, is continued to the target level when a switch-on condition of the compressor (12) is fulfilled, the intermediate level corresponding to the starting level according to speech 1.

6. The method according to one or more of the preceding claims, characterized in that the shutdown condition of the compressor (12) is an upper limit temperature.

7. The method according to claim 6, characterized in that the upper limit temperature is determined directly at the compressor (12) or in the vicinity of the compressor.

8. The method according to one or more of the preceding claims, characterized in that the switch-on condition of the compressor (12) is below the limit temperature.

9. The method according to claim 8, characterized in that the lower limit temperature is determined directly at the compressor (12) or in the vicinity of the compressor.

10. The method according to one or more of the preceding claims, characterized in that the switch-off condition is a lower pressure threshold in the pressure accumulator (3).

11. Level control system of a motor vehicle with at least two axles, at least one air spring (2a, 2b) per axle, possibly one or more drain accumulators (3), at least one pressure sensor (24), means for determining the distance between at least one wheel and / or one Axle and the vehicle body of the motor vehicle (16, 18, 20, 22), a control unit (10) and a compressor (12), the axes being regulated one after the other from a starting level to a target level, the compressor ( 12) is operated and / or a connection is made to at least one air spring (2a, 2b) to the drain accumulator (3) and the upward operation of the air spring (2a, 2b) or air spring (2a, 2b) on an axis from a starting level the control unit (10) cancels to a higher desired level if at least one shutdown condition of the compressor (12) is met and / or the pressure level in the drain accumulator (3) is too low, characterized in that in the control unit (10) a common intermediate height level of all axles or air springs (2a, 2b) with respect to the vehicle body is determined, which is closer to the target level than the starting level, and that the level is on All axles or air springs (2a, 2b) of the motor vehicle are regulated to the common intermediate level, so that the vehicle is no longer at an angle.

12. level control system according to claim 11, characterized in that with the level control system, a method according to claims 2 to 10 is carried out.

13. Level control system according to claim 11 for performing the method according to spoke 7 and / or 9, characterized in that a temperature sensor (26) is arranged on the cylinder head of the compressor (12) or outside or inside the electric motor of the compressor (12).