Method for controlling an air suspension system of a vehicle

Abstract

A method for controlling an air suspension system of a vehicle includes: a) determining a bellows pressure-time characteristic curve for air admission to and release from the bellows of one air spring or the bellows of a plurality of air springs, the characteristic curve being normalized with the value of a supply pressure in a reservoir for compressed air, b) sensor measurement of a current pressure in the spring bellows of the air springs as well as the current supply pressure immediately before air admission thereto or air release therefrom, c) determining, from the normalized characteristic curve, the opening duration for the associated shutoff valve using the ratio of the measured bellows pressure to the measured supply pressure and the ratio of the provided target pressure to the measured supply pressure, d) opening the associated shutoff valve for the determined opening duration in order to set the provided target pressure.

Claims

1. A method for controlling an air suspension system of a vehicle, wherein the system has a changeover valve for each air spring of a vehicle axle or of multiple, adjacent tandem axles, and the system further has a shutoff valve for the air spring of each vehicle wheel of the vehicle axle or for each of the air springs on each vehicle side of the multiple, adjacent tandem axles, wherein the respective changeover valve and the shutoff valves are structurally combined in a valve block arranged remote from the air springs, wherein each of the air springs has a spring bellows and, for measuring a bellows pressure in each of the spring bellows of the air springs, the air suspension system has a respective pressure sensor, the sensors being arranged in or on the valve block, wherein each of the pressure sensors is connected at an outlet of the corresponding shutoff valve to a connection line of the spring bellows of the corresponding air spring or of the spring bellows of the associated air springs, and in which the bellows pressure (p.sub.B) in the spring bellows of the air springs can be set exactly to a target pressure (p.sub.B_2) via measured values of the pressure sensors, wherein the method comprises: a) determining at least one bellows pressure-time characteristic curve (p.sub.B/p.sub.V (t)) for air admission to and air release from the spring bellows of one of the air springs or of the spring bellows of a plurality of air springs, the characteristic curve being normalized with a value of a supply pressure (p.sub.V) in a storage reservoir for compressed air; b) measuring via a sensor a current bellows pressure (p.sub.B_1) in the spring bellows of the air spring or in the spring bellows of the air springs as well as a current supply pressure (p.sub.V_1) immediately before air admission thereto or air release therefrom; c) determining, from the normalized bellows pressure-time characteristic curve (p.sub.B/p.sub.V(t)) for air admission or release, an opening duration (Δt.sub.o) for the corresponding shutoff valve using the ratio of the measured bellows pressure (p.sub.B_1) to the measured supply pressure (p.sub.V_1) and the ratio of the provided target pressure (p.sub.B_2) to the measured supply pressure (p.sub.V_1); and, d) opening the corresponding shutoff valve for the determined opening duration (Δt.sub.o) in order to set a provided target pressure (p.sub.B_2).

2. The method of claim 1, wherein the normalized bellows pressure-time characteristic curves (p.sub.B/p.sub.V (t)) are each determined using different bellows pressure ratios (p.sub.B_1/p.sub.V_1) before air admission or release and using different opening durations (Δt.sub.o) of the associated shutoff valve with a respective target pressure ratio (p.sub.B−2/p.sub.V−1) as the result.

3. The method of claim 1, wherein the normalized bellows pressure-time characteristic curves (p.sub.B/p.sub.V (t)) are determined at the vehicle manufacturers before final inspection of the respective vehicle and are stored in a data memory of an electronic control unit of the vehicle.

4. The method of claim 1, wherein the normalized bellows pressure-time characteristic curves (p.sub.B/p.sub.V (t)) are checked at specified time or mileage intervals during servicing work at a specialist workshop, and are corrected if required.

5. The method of claim 1, wherein the normalized bellows pressure-time characteristic curves (p.sub.B/p.sub.V (t)) are each determined in accordance with a length of the connection line, a diameter of the respective connection line, an existing angle in the run of the connection line, and a volume of the one or more connected spring bellows.

6. The method of claim 5, wherein the bellows pressure-time characteristic curves (p.sub.B/p.sub.V (t)) determined are transferred to combinations of connection lines and spring bellows with the same dimensions.

7. The method of claim 1, wherein separate bellows pressure-time characteristic curves (p.sub.B/p.sub.V (t)) are determined in each case for at least one of certain temperature ranges of the compressed air and different opening combinations of the changeover valves and the shutoff valves.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described with reference to the drawings wherein:

(2) FIG. 1 shows an air suspension system for a vehicle axle of a vehicle having a centralized arrangement of pressure sensors in a schematic view;

(3) FIG. 2 shows the pressure curves for the bellows pressure of a spring bellows and for the pressure detected by a pressure sensor against time during an air admission process in a diagram; and,

(4) FIG. 3 shows the determination of the opening duration of a shutoff valve for the admission of air to a spring bellows via a characteristic curve in a diagram.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) An air suspension system 6, depicted schematically in FIG. 1, for a vehicle axle 2 of a vehicle includes an air spring 8a, 8b having a spring bellows 10a, 10b for each vehicle wheel 4a, 4b of the vehicle axle 2, a valve block 12 having a changeover valve 14, configured as a 3/2-way solenoid switching valve, and a shut off valve 16a, 16b, configured as a 2/2-way solenoid switching valve, for the air spring 8a, 8b of each vehicle wheel 4a 4b, and a pressure sensor 18a, 18b for measuring the bellows pressure in each of the spring bellows 10a, 10b of the air springs 8a, 8b.

(6) Via the changeover valve 14, which is connected by an electric control line 38 to an electronic control unit 36, a working pressure line 20 can be connected alternately to a vent outlet 24 provided with a muffler 26 or to a pressure-carrying supply line 28. A storage reservoir 30 and a pressure sensor 32 are connected to the supply line 28. The pressure sensor 32 measures the supply pressure p.sub.V of the compressed air present in the storage reservoir 30 and is connected by an electric sensor line 42 to the electronic control unit 36. Via the two shutoff valves 16a, 16b, which are connected on the inlet side, via a T piece 22, to the working pressure line 20 and are each connected by an electric control line 40a, 40b to the electronic control unit 36, a respective connection line 34a, 34b leading to the spring bellows 10a, 10b of the associated air spring 8a, 8b can alternately be connected to the working pressure line 20 or shut off from the latter.

(7) In the unactuated, that is, deenergized, state of the changeover valve 14, the working pressure line 20 is connected to the vent outlet 24 and is thus unpressurized. In the actuated, that is, energized, state of the changeover valve 14, the working pressure line 20 is connected to the supply line 28 and is thus under the supply pressure p.sub.V present in the storage reservoir 30.

(8) In the unactuated, that is, deenergized, state of the shutoff valves 16a, 16b, these are in each case closed, and the connection lines 34a, 34b are in this case shut off from the working pressure line 20. To lower the bellows pressure in the spring bellows 10a, 10b of the associated air spring 8a, 8b, all that is required is to open the relevant shutoff valve 16a, 16b, as a result of which air is released from the respective spring bellows 10a, 10b. To increase the bellows pressure in the spring bellows 10a, 10b of the associated air spring 8a, 8b, on the other hand, the switching over of the changeover valve 14 and the opening of the relevant shutoff valve 16a, 16b are required, as a result of which air is admitted to the respective spring bellows 10a, 10b.

(9) The pressure sensors 18a, 18b are arranged in or on the valve block 12 and are each connected at the outlet of the associated shutoff valve 16a, 16b to the connection line 34a, 34b of the spring bellows 10a, 10b of the associated air spring 8a, 8b. The pressure sensors 18a, 18b are configured as pressure-voltage transducers and are each connected to the electronic control unit 36 by a respective electric sensor line 44a, 44b.

(10) As illustrated by way of example in the pressure-time diagram of FIG. 2 for air admission to the spring bellows 10a, 10b of an air spring 8a, 8b, the bellows pressure p.sub.B present in the relevant spring bellows 10a, 10b and the air pressure p.sub.S present at the outlet of the associated shutoff valve 16a, 16b and measured by the associated pressure sensor 18a, 18b deviate to a relatively great extent from one another over the time t during an air admission process since pressure peaks and pressure fluctuations occur at the outlet of the relevant shutoff valve 16a, 16b owing to the opening and closing thereof. Accurate control of air admission and release to and from the spring bellows 10a, 10b on the basis of the sensed air pressures p.sub.S is thus not possible.

(11) The control method described below, which is illustrated in the diagram in FIG. 3, serves to solve this problem. The method envisages that, immediately before air admission to at least one of the spring bellows 10a, 10b of the air springs 8a, 8b, the current bellows pressure p.sub.B_1 in the relevant spring bellows 10a, 10b as well as the current supply pressure p.sub.V_1 are measured via the pressure sensors 18a, 18b, and the bellows pressure ratio p.sub.B_1/p.sub.V_1 before air admission is formed therefrom. Exact determination of the bellows pressure p.sub.B via the associated pressure sensor 18a, 18b is possible since the bellows pressure p.sub.B before air admission is constant, and thus the sensed air pressure p.sub.S is identical with the bellows pressure p.sub.B present in the spring bellows 10a, 10b.

(12) The target pressure ratio p.sub.B_2/p.sub.V_1 is then formed from the provided target pressure p.sub.B_2 up to which air is to be admitted to the spring bellows 10a, 10b and the sensed supply pressure p.sub.V_1. Using the bellows pressure ratio p.sub.B_1/p.sub.V_1 and the target pressure ratio p.sub.B_2/p.sub.V_1, the opening duration Δt.sub.o between two times t.sub.1 and t.sub.2, over which the associated shutoff valve 16a, 16b must be opened, after the switching over of the changeover valve 14, in order to increase the bellows pressure p.sub.B in the relevant spring bellows 10a, 10b from the bellows pressure p.sub.B_1 before air admission to the target pressure p.sub.B_2 after air admission, is then determined from a previously determined bellows pressure-time characteristic curve p.sub.B/p.sub.V (t) normalized with the supply pressure p.sub.V.

(13) In the next step, the changeover valve 14 is switched over, and the associated shutoff valve 16a, 16b is opened for the determined opening duration Δt.sub.o. The setting of the target pressure p.sub.B_2 in the relevant spring bellows 10a, 10b is a relatively accurate process because the air pressure p.sub.S that can be measured with the associated pressure sensor 18a, 18b, which deviates from the bellows pressure p.sub.B in the spring bellows 10a, 10b during the air admission process, is not taken into account.

(14) For air admission to and air release from the spring bellows of an air spring, at least one bellows pressure-time characteristic curve p.sub.B/p.sub.V (t) normalized with the supply pressure p.sub.V is determined in each case. The bellows pressure-time characteristic curves p.sub.B/p.sub.V (t) can preferably be determined at the vehicle manufacturers before final inspection of the respective vehicle and are stored in a data memory of an electronic control unit 36.

(15) 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)

(16) 2 vehicle axle 4a, 4b vehicle wheels 6 air suspension system 8a, 8b air springs 10a, 10b spring bellows 12 valve block 14 changeover valve 16a, 16b shutoff valves 18a, 18b pressure sensors 20 working pressure line 22 T piece 24 vent outlet 26 muffler 28 supply line 30 storage reservoir 32 pressure sensor 34a, 34b connection lines 36 electronic control unit 38 control line 40a, 40b control lines 42 sensor line 44a, 44b sensor lines p pressure p.sub.B bellows pressure p.sub.B/p.sub.V normalized bellows pressure, bellows pressure ratio p.sub.B_1 current bellows pressure p.sub.B_1/p.sub.V_1 bellows pressure ratio before air admission or release p.sub.B/p.sub.V (t) bellows pressure-time characteristic curve p.sub.B_2 target pressure p.sub.B−2/p.sub.V−1 target pressure ratio p.sub.S sensed air pressure p.sub.V supply pressure p.sub.V_1 current supply pressure t time t.sub.1 time, open t.sub.2 time, close Δt.sub.o opening duration