An exemplary embodiment and further advantages of the invention are explained in connection with the following figures in which:
Moreover, with the aid of the compressor 6, compressed air can be transferred out of the atmosphere into each individual pneumatic spring 2a to 2d via the directional valve 34, the air drier 5 and the directional valves 18 and 24a to 24d when the body of the motor vehicle is to be lifted with the aid of compressed air from the atmosphere. Furthermore, compressed air can be discharged from each of the pneumatic springs 2a to 2d into the atmosphere via the directional valves 24a to 24d, 14, the air drier 5 and the directional valve 34 when the body of the motor vehicle is to be lowered and, for this purpose, compressed air is to be discharged into the atmosphere. Further, with the aid of the pressure sensor 30, the pressure both in the compressed air accumulator 4 and in the individual pneumatic springs 2a to 2d can be measured. How the individual functions are implemented and in which switching states the controllable directional valves 14, 18, 24a to 24d and 34 are is not to be dealt with in any more detail here, since it is known per se and is described in detail, for example, in DE 199 59 556 C1. All the functions are brought about by the control unit 36 which, for this purpose, activates the controllable directional valves 14, 18, 24a to 24d and 34 so that these change over to the necessary switching states.
In addition to the abovementioned functions, the air flow L in the level control system can be determined, and in this case it has been shown that a sufficiently accurate determination is possible when the air flow in the compressed air accumulator 4 and in the pneumatic springs 2a to 2d is determined, since the air flow in the compressed air lines is negligible. The air flow L is calculated as follows:
L=p
1
V
1
+p
2
V
2
+p
3
V
3
+p
4
V
4
+p
s
V
s.
With p1 to p4: pressure in the pneumatic springs 2a to 2d;
V1 to V4: volume of a pneumatic springs 2a to 2d;
ps: pressure in the compressed air accumulator 4;
Vs: volume of the compressed air accumulator 4.
The determination of the air flow L in a closed level control system is known per se and is described in detail, for example, in DE 101 22 567 C1. It can be gathered from the equation for determining the air flow L that the air flow L is dependent on the temperature (since the individual addends pV are dependent on the temperature according to the ideal gas law). A rise in the temperature signifies a rise in the air flow, and a lowering of the temperature signifies a lowering of the air flow.
When compressed air is discharged from the level control system into the atmosphere via the air drier 5, the air drier is regenerated. The regeneration of the air drier 5 is carried out when compressed air has previously been transferred from the atmosphere into the level control system, since the moisture in the air drier thereby rises. It is explained below how regeneration is carried out in detail: first, before the level control system is filled up with compressed air, the air flow L1 in the level control system is determined. Then, compressed air is transferred out of the atmosphere into the level control system via the air drier 5. When sufficient compressed air has been transferred into the level control system, the air flow L2 in the level control system is determined. Then, the differential air flow ΔL=L1−L2 is determined, and, by means of the differential air flow ΔL, a regeneration air flow is determined, which is necessary in order to regenerate the air drier 5 (the determination of the regeneration air flow may additionally include information on the air drier 5). In a further step, at least the regeneration air flow is transferred out of the atmosphere into the level control system via the air drier 5 and is thereafter discharged into the atmosphere again via the air drier 5 for the regeneration of the latter. Such a procedure has the advantage, inter alia, that, on the one hand, the air flow is transferred out of the atmosphere to the level control system which is necessary there independently of the regeneration of the air drier 5 (since, for regeneration, an additional air flow from the atmosphere is transferred into the level control system) and, on the other hand, the air drier 5 is regenerated.
It is explained below, in connection with
A first air flow interval I1 may be gathered from
The control of the air flow L in the level control system is carried out as follows by means of the control unit 36: it is assumed that the currently determined air flow L in the level control system lies below the lower limit U2 of the air flow interval I2, as is indicated by the dot 38. In this case, the control unit 36 brings about a rise in the air flow, specifically until the current air flow L lies within the air flow interval I2. Preferably, control is carried out in such a way that, after control, the air flow L in the level control system lies between U1 and U2, as is indicated by the dot 40 (the control operation is indicated by the arrow 42). In this control, an increase in the air flow takes place in that the compressed air accumulator 4 is filled from the atmosphere by means of the compressor 6 via the directional valves 34 and 18 (see
It is likewise possible that the current air flow L in the level control system lies above the upper limit O2 of the air flow interval I2, as is indicated by the dot 44. In this case, the control unit 36 causes the air flow L to be reduced until the current air flow L lies within the second air flow interval I2. Preferably, in this case, the air flow L is reduced until the current air flow L lies between O1 and O2, as is indicated by the dot 46 (the control operation is indicated by the arrow 48). The reduction in the air flow L is brought about by the control unit 36 and leads to compressed air being discharged into the atmosphere from the compressed air accumulator 4 by the directional valves 14 and 34 (see
The control operations, indicated by the arrows 42 and 48, in which the current air flow L lay outside the second air flow interval I2 before control, are carried out in any event and at any time (that is to say, independently of the operating state of the motor vehicle; the control operations are therefore carried out both when the motor vehicle is out of operation (which may be detected, for example, from the fact that the engine is not running) and when the motor vehicle is in operation), when a corresponding air flow L is detected.
By contrast, a control of the air flow L takes place solely under specific preconditions when the air flow lies outside the first air flow interval I1 and within the second air flow interval I2 before control. If the preconditions are not fulfilled, control does not take place. This is explained below: it is assumed that, before control, a current air flow L is detected which lies below the lower limit U1 of the air flow interval I1 and above the lower limit U2 of the air flow interval I2, as is indicated by the dot 50. In this case, under specific preconditions, a control of the air flow L into the first air flow interval I1 is carried out, as is indicated by the dot 52 (the operation is indicated by the arrow 54). Preferably, in this case, the air flow L is increased until the current air flow L in the level control system lies in the middle (indicated by the dashed line) of the air flow interval I1. This achieves the advantage that, after the control of the air flow L, the latter has the highest possible fluctuation width, without departing from the air flow interval I1. Further adjustment is therefore required only rarely. The rise in the air flow L in the level control system takes place exactly as has already been explained above in connection with the control operation from the dot 38 to the dot 40.
It is likewise possible that the current air flow L lies above the upper limit O1 and below the lower limit O2 as is indicated by the dot 56. In this case, when specific preconditions are fulfilled, the current air flow L in the level control system is reduced until this lies in the air flow interval I1, as is indicated by the dot 58 (the associated control operation is indicated by the arrow 60). In this case, too, preferably sufficient compressed air is discharged from the level control system until the current air flow L in the level control system lies in the middle of the air flow interval I1, in order to achieve the abovementioned advantage. The discharge of the compressed air from the level control system takes place exactly as has already been explained in connection with the control operation from the dot 44 to the dot 46 (see above).
The preconditions which must be fulfilled so that the control unit 36 (see
The list is illustrative, and further alternative preconditions may be envisaged.
After control into the first air flow interval I1 has taken place in the presence of the fixed precondition, control of the air flow takes place as long as the motor vehicle is in operation, in such a way that the air flow remains in the first air flow interval I1 during operation. Only when the control unit 36 detects that the motor vehicle is no longer in operation does the control unit 36 allow the air flow L to depart from the air flow interval I1.
When the air flow L is located in the air flow interval I1, the level control system has a high control speed, that is to say the body of the motor vehicle can be both lifted and lowered quickly. If the air flow L is located outside I1, control into the air flow interval I1 takes place when the fixed precondition (see above) is fulfilled. As long as the motor vehicle is in operation, control of the air flow L takes place in such a way that (after the air flow has been controlled into I1) the air flow remains in I1. A high control speed is consequently ensured while the motor vehicle is in operation.
(It is assumed, in the example, that the first precondition that the motor vehicle is put into operation is fixed in the control unit.)
When the motor vehicle is stopped at a parking place on a hot summer's day, it heats up sharply, and it may happen that the air temperature in the level control system rises above 35° C. and therefore the current air flow in the level control system lies above the upper limit O1. As long as the current air flow lies between O1 and O2 when the motor vehicle is at a standstill, no control of the air flow takes place. If, however, the air flow lies above O2 (the temperature therefore rises above 50° C.), control is carried out by the control unit 36 (see
Compressed air can likewise be transferred via the nonreturn valve 62 out of the atmosphere directly into one or more of the pneumatic springs 2a to 2d via the compressor 6, in order to lift the level of the motor vehicle. This is necessary particularly when the air flow L in the level control system lies below the second lower limit U2 and the level of the motor vehicle is below a safe level. In this case, the motor vehicle is first lifted to a safe level, and then control of the air flow L is carried out in such a way that, after control, the air flow L again lies at least above the second lower limit U2 (preferably, control of the air flow L is carried out in such a way that the air flow L lies above the first lower limit U1 again after control). In this case, to lift the motor vehicle to the safe level, first, the compressed air located in the compressed air accumulator 4 is used (this takes place, as has already been explained in connection with
The above statements show that the compressed air is transferred into one or more of the pneumatic springs 2a to 2d from the atmosphere directly, that is to say without previously being led via the air drier 5. This means that the compressed air has not been dried, and therefore the moisture in the air flow L of the level control system rises. The following procedure is adopted in order to compensate this rise: immediately before compressed air is transferred into the level control system via the nonreturn valve 62, the air flow L1 in the level control system is determined. Then, compressed air is transferred out of the atmosphere via the nonreturn valve 62 directly into one or more of the pneumatic springs 2a to 2d, until the motor vehicle has reached the safe level. After the conclusion of the operation of lifting the motor vehicle, the air flow L2 in the level control system is determined, and then the differential air flow ΔL=L1−L2 is determined (the determination of the air flows L1, L2 and ΔL takes place, as has already been explained in connection with
For regenerating the air drier 5, compressed air is discharged later into the atmosphere from the compressed air accumulator 4 via the air drier 5 and the controllable directional valve 64. For this purpose, the control unit 36 activates the directional valve 64 so that the latter changes over from the switching state shown in
The scavenging air quantity may be transferred from the atmosphere into the compressed air accumulator 4 via the nonreturn valve 62, the compressor 6, the directional valve 18 and the air drier 5 in a single step or in a plurality of cycles.
In addition to this scavenging air flow, an air flow Lz is transferred out of the atmosphere into the compressed air accumulator 4 via the nonreturn valve 62, the compressor 6, the directional valve 18 and the air drier 5. The air flow Lz is dimensioned such that, after the transfer of this air flow Lz, the entire air flow L in the level control system lies at least above the second lower limit U2 again (preferably, the air flow Lz is dimensioned such that, after the transfer of this air flow Lz, the entire air flow L in the level control system lies above the first lower limit U1 again; as a reminder: in the exemplary embodiment described, it was assumed that the total air flow L lies below the second lower limit U2 and the motor vehicle is below a safe level).
2
a, . . . , 2d Pneumatic spring
4 Compressed air accumulator
5 Air drier
6 Compressor
8 Inlet of the compressor
10 Outlet of the compressor
14 Controllable directional valve
18 Controllable directional valve
24
a, . . . , 24d Controllable directional valves
30 Pressure sensor
34 Controllable directional valve
36 Control unit
38 Dot
40 Dot
42 Arrow
44 Dot
46 Dot
48 Arrow
50 Dot
52 Dot
54 Arrow
56 Dot
58 Dot
60 Arrow
62 Nonreturn valve
64 Controllable directional valve
Number | Date | Country | Kind |
---|---|---|---|
103 43 094.6 | Sep 2003 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/EP04/06709 | 6/22/2004 | WO | 00 | 4/30/2007 |