The invention relates to a method for controlling the quantity of air in a self-contained air supply system for a chassis. Such air supply systems are used, for example, for controlling the required level of motor vehicles.
Such an air supply system is known from EP 1 243 447 A2. According to its
DE 101 22 567 C1 discloses a further method for controlling the quantity of air in which the influence of the instantaneous load on the control of the quantity of air is excluded and control of the quantity of air is therefore carried out only when there is a deviation from the design-rated quantity of air band due to leakage or temperature fluctuation. In this context, the instantaneous quantities of compressed air in the air accumulator and in the air springs are determined by measuring the pressures using a pressure sensor and multiplying them by the known volume of the air accumulator and by the volume of the air springs determined by a travel measurement. This quantity of compressed air which is determined in this way for the air supply system is compared with the optimum quantity of compressed air for a design-rated load. If the quantity of compressed air which is determined is smaller than a minimum necessary quantity of compressed air, a specific quantity of compressed air must be added, and if it is larger than a maximum admissible quantity of compressed air a specific quantity of compressed air must be let out. The time necessary to add air or let air out is determined from a known controlling speed compressed air quantity characteristic curve and the corresponding valves or the compressor in the air supply system are activated for this time period. This method also requires the presence of a pressure sensor with all its disadvantages which have already been described. In addition, this method is relatively complex in terms of software technology because the actual volume quantity always has to be calculated in order to determine the time necessary to add or let out air.
The object is therefore to simplify the method of the generic type for controlling the quantity of air in a closed air supply system.
This object is achieved by a method in which the demand for or the excess of a necessary quantity of compressed air for the air supply system is determined for a prescribed design case and is fed into the air supply system or let out of it over a defined time. According to the invention, an average controlling speed is calculated from a defined movement of the air springs and is compared with an optimum controlling speed, the demand for or the excess of a quantity of compressed air being determined from the comparison between the controlling speeds.
The new method eliminates the aforesaid disadvantages of the prior art. The particular advantage of the new method here is that in order to determine the deficit or the excess in terms of the quantity of compressed air it is no longer necessary to carry out a complex pressure measurement but rather all that is necessary is to measure the travel and/or the time required to carry it out during a raising and/or lowering process. Such a travel measurement or time measurement is possible with relatively simple means which generally form part of the technical equipment of the system. This simplifies the equipping of the air supply system and reduces the costs necessary to do so. This expenditure on equipment can also be reduced further if for example the travel is predefined for the movement of the air spring. Then only the time has to be measured. The new method for controlling the quantity of air can of course also be applied in other air supply systems.
The new method will be explained in more detail with reference to a plurality of exemplary embodiments.
In the drawings,
As is shown by
In order to fill the air accumulator 5 with fresh air from the atmosphere, the two intake side 2/2 way valves 12, 16 and the pressure side 2/2 way valve 15 as well as the blow off valve 14 are closed and the first pressure side 2/2 way valve 11 is opened. The compressor 6 sucks in the fresh air from the atmosphere via the intake valve 7 and feeds it into the air accumulator 5 via the air drier 9, the opening throttle nonreturn valve 10 and the opened first pressure side 2/2 way valve 11. In order to fill the air springs 3, 4 with compressed air from the air accumulator 5, the first pressure side 2/2 way valve 11, the second intake side 2/2 way valve 16 and the blow off valve 14 are closed. In contrast, the first intake valve 2/2 way valve 12 and the second pressure side 2/2 way valve 15 of the compressor 6 are opened so that the compressor 6 sucks in the air from the air accumulator 5 and feeds it to the air springs 3, 4 via the actuator pressure line 13 and the nonreturn valve combination 2. In order to transfer dried compressed air which is not required from the air springs 3, 4 into the air accumulator 5, the first intake side 2/2 way valve 12, the second pressure side 2/2 way valve 15 and the blow off valve 14 are closed and the second intake side 2/2 way valve 16 and the first pressure side 2/2 way valve 11 are opened. As a result, the air from the air springs 3, 4 passes into the air accumulator 5 via the nonreturn combination 2, the compressor 6 and the first pressure side 2/2 way valve 11. In order to regenerate the drier 10 with dried compressed air which is not required from the air pressure accumulator 5, the two intake side 2/2 way valves 12, 16 and the second pressure side 2/2 way valve 15 are closed and the first pressure side 2/2 way valve 11 and the blow off valve 14 are opened. As a result, air is fed into the atmosphere counter to the filling direction from the air accumulator 5 via the accumulator pressure line 8, the throttled throttle nonreturn valve 10, the air drier 9, the actuator pressure line 16 and the blow off valve 14.
In order to safeguard all these functions it is necessary for a sufficient quantity of compressed air to be present within a quantity of air tolerance band in the air supply system for a design-rated vehicle load. If the quantity of compressed air drops below the design rating, outside the air quantity tolerance band, the air supply system must be topped up with a necessary quantity of compressed air. In contrast, if the design rated quantity of compressed air is exceeded outside the quantity of air tolerance band, a specific quantity of compressed air is let out of the air supply system. In both cases the loaded vehicle body is raised or lowered with a toleranced speed.
The new method is presented for controlling the quantity of air in the self-contained air supply system in a first exemplary embodiment. Here, the quantity of compressed air for supplying the air supply system is firstly defined in such a way that at the specific design load the pressures in the air accumulator 5 and in the air springs 3, 4 are the same so that when there is a connection between the air accumulator 5 and the air springs 3,4 the air springs 3,4 are not displaced. In order to determine the deviation of the quantity of compressed air from the tolerance band of the quantity of compressed air in a design rating, all the intake side and pressure side 2/2 way valves 11, 12, 15, 16 are opened, while the blow off valve 14 remains closed. As a result, the air springs 3, 4 and the air accumulator 5 are connected to one another in such a way that a quantity of air can be exchanged in both directions. Depending on the load at the air springs 3, 4, the air springs 3, 4 experience spring compression below the normal height level NN as is shown in
Air springs 3, 4 which have experienced spring compression are raised again to the normal height level NN directly afterwards using the compressor 6 according to
The air quantity in the self-contained air supply system can also be controlled according to the new method with a second exemplary embodiment. To do this, the raising speeds of an idling load, of a full load and of a design rating load must firstly be determined empirically from the normal height level NN over a predetermined distance with difference pressures in the air accumulator 5 and are illustrated in a diagram. Such a diagram is illustrated in
In order to control the quantity of compressed air for the air supply system which is in operation, in a current load situation a defined raising process carried out over a predetermined amount of travel. The time required for this is measured and the average current raising speed is calculated from the defined travel and the time required. This rating speed is compared with all three load characteristic curves for the no load situation, the design rating load and the full load using the diagram according to
The control of the air quantity in the self-contained air supply system according to the new method can also be performed with a third exemplary embodiment. This exemplary embodiment is applied if the pressure in the air accumulator 5 is lower than the pressure in the air springs 3, 4. At first, an enclosed control space is selected within the air supply system, for which purpose the crank casing of the compressor 6 and the air drier 6 are most suitable. This control space is placed at a defined pressure level. It is thus expedient to connect this control space to the atmosphere using the 2/2 way valve 14 so that the atmospheric pressure is set in the control space. The 2/2 way valve 16 is then opened for a defined time so that a quantity of compressed air flows from the air springs 3, 4 with the higher pressure into the control space with the lower pressure until the pressure is equalized. Then, the air supply system is re-activated until the vehicle axle is located in the NN home position again. Here, the travel carried out by the air springs 3, 4 and the time required to do this are measured. An average raising speed is calculated from this travel and the measured time. Depending on the load state a characteristic speed range Vmin≦v≦vmax are calculated from a simulation or from a measurement. The calculated raising speed is then compared with the admissible raising speeds. If it is determined that the calculated raising speed lies within the admissible raising speeds Vmin≦v≦vmax, a sufficient quantity of compressed air is present. If the calculated raising speed is below the admissible raising speed Vmin, an excessively low quantity of compressed air is present in the air supply system. For a defined time, the compressor 6 and the corresponding 2/2 way valves are activated and air is fed into the air accumulator 5 from the surroundings. The converse occurs if the calculated raising speed is above the admissible raising speed vmax, and an excessively large quantity of compressed air is then present in the air supply system. The corresponding 2/2 way valves are activated again for a defined time in order to emit air into the surroundings from the air accumulator 5. The air supply system then contains again a quantity of compressed air which is within the band for the quantity of compressed air for the design rating.
Number | Date | Country | Kind |
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10 2004 021 592.8 | May 2004 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2005/051186 | 3/16/2005 | WO | 00 | 11/3/2006 |