METHOD FOR CONTROLLING THE PRESSURE OF AN AIR BELLOWS

Abstract

A method is for regulating the pressure of an air bellows belonging to an air suspension, a determination of a filling pressure generatable inside the bellows by a filling process takes place with a learning algorithm as well as via a pressure and a height measuring sensor. The pressure sensor is arranged in a feed line leading to the bellows. Before opening the valve, in successive cyclic pressure and height measurements and on the basis of a characteristic curve, in which a characteristic number as a variable representative of a bellows volume V is plotted against the bellows height, a flow rate at the bellows inlet is ascertained and an air mass flow in the line between the valve and the bellows is ascertained therefrom, integrated and added to the bellows air mass. A new filling pressure is ascertained via the algorithm.

Claims

1. A method for regulating a pressure of an air bellows belonging to a pressure-regulated air suspension, wherein a determination of a filling pressure that can be generated inside the air bellows by a filling process takes place with the aid of a learning algorithm programmed in an associated computing device as well as via a pressure measuring sensor and a height measuring sensor, the computing device being assigned to a control device for controlling switching processes of valves in the air suspension, wherein the pressure measuring sensor is arranged at a distance from the air bellows in a feed line leading to the air bellows through which an air mass flow can be delivered under pressure into the air bellows, wherein a valve, which can be switched between a shut-off setting and an open setting for filling or venting the air bellows, is provided in the feed line and the pressure measuring sensor is arranged between the valve and the air bellows, the method comprising: before the valve is opened in order to fill the air bellows: a) taking a first measurement of a first pressure p.sub.0 at the pressure measuring sensor; b) taking a first measurement of a current first height h.sub.0 of the air bellows by the height measuring sensor; c) on a basis of a characteristic curve determined by predefined starting values, in which a dimensionless characteristic number K.sub.V as a variable representative of a bellows volume V is plotted against a height of the air bellows, determining an assumed starting air mass m.sub.0 in the air bellows with the first pressure p.sub.0, the first height h.sub.0 and with a characteristic number K.sub.V0 obtained for the first height h.sub.0 from the characteristic curve as a variable representative of a bellows volume V.sub.0; opening the valve in order to fill the air bellows; after said opening the valve in order to fill the air bellows, while the valve is open, respectively in a number of successive cycles within cycle times of the cycles: d) taking a further measurement of a further pressure p.sub.1 at the pressure measuring sensor; e) from a pressure difference between the pressure p.sub.1 measured in step d) and the pressure p.sub.0 measured in step a), ascertaining a flow rate of air at a bellows inlet corresponding to the pressure difference with the aid of the algorithm and ascertaining the air mass flow in the feed line between the valve and the air bellows therefrom; f) integrating the air mass flow ascertained in step e) over a cycle time to give a differential air mass and added to the assumed starting air mass m.sub.0 in the air bellows, determined in step c), to give a bellows air mass m.sub.B assumed after the cycle time; g) taking a further height measurement of a current height h.sub.1 of the air bellows by the height measuring sensor and ascertaining a new filling pressure p.sub.B to be assumed in the air bellows and resulting from the air mass feed during a preceding cycle with the aid of the algorithm from a characteristic number K.sub.V1 ascertained for the height h.sub.1 with aid of the characteristic curve as a variable representative of a bellows volume V.sub.1 and the bellows air mass m.sub.B totaled in step f); h) repeating steps d) to g) within each further individual cycle time, the totaled bellows air mass m.sub.B respectively ascertained in the preceding cycle being used as the basis in step f) as a new starting air mass m.sub.0=m.sub.B respectively contained in the air bellows; and, wherein the new filling pressure p.sub.B respectively ascertained in the steps d) to h) is provided as an input signal of an electronic regulating device for filling the air bellows, the valve being closed by the regulating device, and the determination of the filling pressure for the filling process being ended, after a predefined target pressure in the air bellows is reached.

2. The method of claim 1, wherein the cycle times for carrying out all of steps d) to g) while the valve is open are 25 milliseconds.

3. The method of claim 1, wherein a predefined diameter norm of the feed line is used as the basis for ascertaining the air mass flow in step e).

4. The method of claim 1, wherein the characteristic curve is determined by at least two predefined starting value pairs for the characteristic number K.sub.V and the respectively associated height of the air bellows.

5. The method of claim 1, further comprising taking a further measurement of a pressure p.sub.opt at the pressure measuring sensor and a further measurement of a height h.sub.opt of the air bellows following the filling of the air bellows; wherein with the bellows air mass m.sub.B in the air bellows ascertained after a previous filling process, the pressure p.sub.opt and the height h.sub.opt, a characteristic number K.sub.opt corresponding to measurement values of the pressure p.sub.opt and the height h.sub.opt is ascertained as a variable representative of an optimized bellows volume and is entered into the characteristic curve as a learned characteristic number belonging to the height h.sub.opt, in place of the former characteristic number contained there.

6. The method of claim 5, wherein the characteristic number K.sub.opt is ascertained at the earliest 400 milliseconds after the valve is closed.

7. The method of claim 5, wherein the learned characteristic number K.sub.opt belonging to the height h.sub.opt, as a variable representative of the optimized bellows volume, is used as a basis for ascertaining the starting air mass m.sub.0 in step a) during a fresh valve opening instead of a hitherto existing or ascertained characteristic number as a variable representative of a new bellows volume.

8. The method of claim 5, wherein the characteristic curve is adapted by extrapolating the characteristic number K.sub.opt respectively ascertained for the highest measured height h.sub.opt of the air spring as a variable representative of the optimized bellows volume as an ordinate value to an end of the height values plotted on an abscissa.

9. The method of claim 1 wherein in method steps c) and g) during raising or lowering of a lift axle, both for a support bellows assigned to the lift axle and for a lift bellows, a constant characteristic number K.sub.V-lift as a variable representative of the bellows volume V being constant is plotted against the height of the air bellows and is assumed for the entire inflation process.

10. The method of claim 3, wherein the predefined diameter norm is 1.

11. A method for regulating the pressure of an air bellows belonging to a pressure-regulated air suspension, wherein the determination of a pressure resulting from a venting process inside the air bellows takes place with the aid of a learning algorithm programmed in an associated computing device as well as via a pressure measuring sensor and a height measuring sensor, the computing device being assigned to a control device for controlling switching processes of valves in the air suspension, wherein the pressure measuring sensor is arranged at a distance from the air bellows in a feed line leading to the air bellows, through which an air mass flow can be delivered under pressure from the air bellows, wherein a valve, which is configured to be switched between a shut-off setting and an open setting for filling or venting the air bellows, is provided in the feed line and the pressure measuring sensor is arranged between the valve and the air bellows, the method comprising: before the valve is opened in order to vent the air bellows: a) taking a first measurement of a first pressure p.sub.0 at the pressure measuring sensor, and b) taking a first measurement of a current first height h.sub.0 of the air bellows by the height measuring sensor; and, c) determining, on a basis of a characteristic curve determined by predefined starting values, in which a dimensionless characteristic number K.sub.V as a variable representative of a bellows volume V is plotted against a height of the air bellows, an assumed starting air mass m.sub.0 in the air bellows takes place with the first pressure p.sub.0, the first height h.sub.0 and with a characteristic number K.sub.V0 obtained for the first height h.sub.0 from the characteristic curve as a variable representative of a bellows volume V.sub.0; opening the valve in order to vent the air bellows; while the valve is open, respectively in a number of successive cycles within the cycle times: d) taking a measurement of a further pressure p.sub.1 at the pressure measuring sensor; wherein e) from the difference between the pressure p.sub.1 measured in step d) and the pressure p.sub.0 measured in step a), ascertaining a flow rate of air at a bellows outlet corresponding to the pressure difference (p.sub.0p.sub.1) with the aid of the learning algorithm and air mass flow in the feed line between the air bellows and the valve is ascertained therefrom, the air mass flow being multiplied by a correction factor k.sub.vent that takes into account a friction loss in the feed line; after which: f) integrating the air mass flow ascertained in step e) and provided with a correction factor over a cycle time to give a differential air mass and subtracted from the assumed starting air mass m.sub.0 in the air bellows, which was determined in step c), to give a bellows air mass m.sub.B assumed after the cycle time; g) taking a further measurement of a current height h.sub.1 of the air bellows by the height measuring sensor and ascertaining a new filling pressure p.sub.B to be assumed in the air bellows and resulting from an air mass discharge during the preceding cycle with the aid of the algorithm from a characteristic number K.sub.V1 ascertained for the height h.sub.1 with the aid of the characteristic curve as a variable representative of a bellows volume V.sub.1 and the bellows air mass m.sub.B ascertained in step f); h) repeating steps d) to g) within each further individual cycle time, the ascertained bellows air mass m.sub.B respectively ascertained in the preceding cycle being used as the basis in step f) as a new starting air mass m.sub.0=m.sub.B respectively contained in the air bellows; wherein the new filling pressure p.sub.B respectively ascertained in the steps d) to h) is provided as an input signal of an electronic regulating device for venting the air bellows, the valve being closed by a regulating device, and the determination of the bellows pressure for the venting process being ended, after a predefined target pressure in the air bellows is reached.

12. The method of claim 11, wherein as an initial value the air mass flow is multiplied by a correction factor k.sub.vent=1.

13. A device for regulating the pressure of at least one air bellows belonging to a pressure-regulated air suspension, wherein a determination of a filling pressure that can be generated inside the air bellows by a filling process takes place with the aid of a programmed learning algorithm, the device comprising: a control device for controlling switching processes and valves as well as a computing device assigned to the control device with the programmed learning algorithm; a pressure measuring sensor and a height measuring sensor assigned to the at least one air bellows; said pressure measuring sensor for measuring the air bellows pressure being arranged at a valve arranged in a feed line to the at least one air bellows and at a distance from the at least one air bellows; an air mass flow can be delivered under pressure in the feed line into the air bellows or from the air bellows and the valve is configured as a directional control valve and is configured to be switched to a shut-off setting, an inflation setting and a venting setting in order to fill or vent the air bellows via the feed line, wherein the pressure measuring sensor is arranged at a valve outlet of the valve which leads to the feed line to the air bellows.

14. The device of claim 13, wherein a valve block is arranged at a start of the feed line to the air bellows, which lies remotely from the air bellows.

15. A leveling apparatus in a commercial vehicle with air suspension, the leveling apparatus comprising the device of claim 13.

16. The leveling apparatus of claim 15, wherein the commercial vehicle is a truck or a commercial vehicle trailer.

17. A control device for a leveling apparatus in a commercial vehicle with air suspension, the control device comprising the computing device in which the learning algorithm for carrying out the method of claim 1 is programmed.

18. An air-suspended vehicle comprising the device of claim 13.

19. The air-suspended vehicle of claim 17, wherein the vehicle is an air-suspended truck or an air-suspended trailer.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0074] The invention will now be described with reference to the drawings wherein:

[0075] FIG. 1 shows with the aid of a diagram an equivalent model on which the method according to the disclosure is based;

[0076] FIG. 2 shows a schematic diagram of the essential elements of a device for carrying out the method according to the disclosure;

[0077] FIG. 3 shows a characteristic curve assumed at the beginning of the ascertainment by the method according to the disclosure;

[0078] FIG. 4 shows a characteristic curve obtained after a plurality of filling and venting processes and approximated to the real conditions by the method according to the disclosure;

[0079] FIG. 5 shows a comparison of the characteristic curves according to FIGS. 3 and 4; and,

[0080] FIG. 6 shows a block diagram to illustrate individual method steps.

DETAILED DESCRIPTION

[0081] FIG. 1 shows with the aid of a diagram an equivalent model, on which the method according to the disclosure is based, for determining a filling pressure that can be generated by a filling process. It shows a stylized air bellows 1, replaced by a piston-cylinder model, having an associated feed line 2 and a pressure measuring sensor 3. During filling, an air mass flow t is created in the feed line 2. The air, or air quantity or air mass, 4 necessary for the filling is delivered from a pressure source (not represented in detail), that is, from a compressor or from a pressure accumulator, via a valve into the feed line 2. At the start of the feed line 2, that is, separated from the air bellows 1 by the feed line length L, the medium pressure/air pressure existing in the feed line 2 is measured with the aid of the pressure measuring sensor 3. The height h corresponds to the height of the air bellows as measured by a height measuring sensor, and the volume V contained in the piston-cylinder model corresponds to the air spring volume.

[0082] FIG. 2 shows in the form of a schematic diagram essential elements of a device for carrying out the method according to the disclosure, such as are arranged and required for a pressure-regulated air suspension in a commercial vehicle with a driven rear axle 5 and a non-driven front axle 6. The rear axle 5 and the front axle 6 are represented merely symbolically in FIG. 2 by the arrangement of air springs/air bellows 7 as well as by a single tire on the front axle with the tires 8 and by twin tires on the driven rear axle with the tires 9.

[0083] The supply pressure for the air bellows 7, or air springs, is generated by a compressor (not represented in detail) that fills a pressure accumulator 10 via which the individual air springs 7 can also be supplied with air.

[0084] In order to regulate the filling, and therefore to regulate the air suspension, a leveling apparatus is provided, which has inter alia solenoid valves, namely switchable valves 11 with the respectively associated electromagnetic actuation devices 12. The supply lines, or feed lines 13, from the solenoid valves 11, 12 to the air bellows 7 are also shown. The valves 11 are configured as directional control valves, and can be switched to a shut-off setting, an inflation setting and a venting setting in order to fill or vent the respective air bellows 7 via the feed lines 13.

[0085] There are also data lines 14 to a control device 15 of the leveling apparatus, as well as a data line 19 between the electronic circuits provided at the valves 11, 12. The data line 19 subserves the communication between the valves as well as between the valves and the control device 15. Further data lines 16 connect the height measuring sensors 17 to the control device 15 by using electronic circuits at the valves.

[0086] Compressed-air supply pressure lines 18 are furthermore represented, which are connected to the feed lines 13 via the switchable solenoid valves 11, 12 so that the air springs/air bellows 7 can be filled or vented.

[0087] The switchable solenoid valves 11, 12 may be arranged in a valve block in which a plurality of different valves of the control loop are combined. The electromagnetic actuation devices 12, the valves 11 and the electronic component parts provided at the valves are respectively fitted together in a compact housing.

[0088] By using the control device 15, the valves 11, 12 are switched while taking into account the signals of the height measuring sensors 17 and of the pressure sensors (not represented separately here) within the valve block. The control device 15 contains an associated computing device with a programmed learning algorithm.

[0089] The pressure measuring sensors are located at the outlets of the valves 11, 12 to the feed lines 13 and are thus arranged at a distance from the respective air bellows 7, at the start of the associated feed line 13. For the sake of clarity, the pressure measuring sensors have not been represented in detail in FIG. 2.

[0090] The filling of an air bellows with the leveling apparatus then takes place by the method according to the disclosure with initial use of a characteristic curve for an air bellows, as is represented in FIG. 3.

[0091] FIG. 3 shows the characteristic curve 20 assumed at the beginning of the ascertainment by the method according to the disclosure, namely the ratio of the height of the air bellows 21 to the characteristic number 22 for the bellows volume. The characteristic curve is predefined by two characteristic curve points/curve points, which are not represented in detail here.

[0092] FIGS. 4 and 5 also show characteristic curves, which indicate the ratio of the height of the air bellows 21 to the characteristic number 22 for the bellows volume.

[0093] FIG. 4 shows a characteristic curve 23 obtained after a plurality of filling and venting processes by the method according to the disclosure and approximated to the real conditions, which is then used as the basis for the further determinations according to the disclosure of the filling pressure in the bellows.

[0094] FIG. 5 shows the characteristic curve 20 in comparison with the characteristic curve 23 ultimately obtained by the method according to the disclosure, adapted to the real conditions, the two characteristic curves being represented here on a different scale, however, and over the total working height of the air bellows.

[0095] FIG. 6 illustrates once more with the aid of a block diagram the individual method steps a) to h) which are controlled by the algorithm that is programmed in the computing device R1 of the control device 15. The control device, or the algorithm, then also initiates the action A1, that is, the opening of the solenoid valve, as well as the action A2, that is, the closing of the valve. It also indicates the use of characteristic curves 20, 23 as representative variables during the determination of a filling pressure that can be generated inside the air bellows by a filling process.

[0096] 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 SIGNS (PART OF THE DESCRIPTION)

[0097] 1 air bellows, represented as an element of a piston-cylinder model [0098] 2 feed line [0099] 3 pressure measuring sensor [0100] 4 air quantity [0101] 5 rear axle [0102] 6 front axle [0103] 7 air bellows, air spring [0104] 8 tiressingle tire [0105] 9 tirestwin tires [0106] 10 pressure accumulator [0107] 11 switchable valve [0108] 12 electromagnetic actuation device [0109] 13 supply line/feed line [0110] 14 data line [0111] 15 control device, vehicle controller [0112] 16 data line [0113] 17 height measuring sensor [0114] 18 compressed-air supply line [0115] 19 data line [0116] 20 starting characteristic curveratio of the height of the air bellows to the number characteristic of the bellows volume [0117] 21 abscissa of the characteristic curveheight of the air bellows [0118] 22 ordinate of the characteristic curvenumber characteristic of the bellows volume [0119] 23 characteristic curveratio of the height of the air bellows to the number characteristic of the bellows volume [0120] h height of the air bellows (in the piston-cylinder model) [0121] V air spring volume (in the piston-cylinder model) [0122] L line length (in the piston-cylinder model) [0123] A1 action: open valve [0124] A2 action: close valve [0125] R1 computing device with programmed algorithm