METHOD FOR LEAKAGE MONITORING OF A COMPRESSED-AIR SYSTEM

Abstract

A method for leakage monitoring of a compressed air system of a motor vehicle is disclosed. The compressed-air system has a compressed air supply system, a compressor, and a plurality of compressed-air consumer circuits. The method includes: a) successive detection of a supply pressure via a pressure sensor in a main supply line or in a supply line of at least one compressed air consumer circuit at a predefined time interval; b) successive calculation of pressure gradients of the supply pressure from at least two consecutively detected pressure values; c) comparison of the determined pressure gradients with a predefined gradient limit value; and d) output of a warning signal when the pressure gradient within a predefined monitoring time period which comprises a plurality of delivery pauses of the compressor has not exceeded the gradient limit value.

Claims

1. A method for leakage monitoring of a compressed air system of a motor vehicle, the compressed air system having a compressed air supply system, a compressor connected on an input side thereto, and a plurality of compressed air consumer circuits connected on an output side thereto, said method comprising: a) continuously detecting by sensor a supply pressure via a pressure sensor in a main supply line or in a supply line of at least one compressed air consumer circuit in a predefined time interval, b) continuously calculating the pressure gradients of the supply pressure from in each case at least two successively detected pressure values and the a time difference Δt between the detection thereof at least during delivery pauses of the compressor, c) comparing the determined pressure gradients with a predefined gradient limit value, and d) outputting a warning signal when the pressure gradient within a predefined monitoring time period, which comprises a plurality of delivery pauses of the compressor, has not exceeded the gradient limit value.

2. The method as claimed in claim 1, wherein pressure fluctuations of the supply pressure which are attributable to thermodynamic effects occurring in the compressed air consumer circuits are eliminated.

3. The method as claimed in claim 2, wherein the pressure values detected by sensor and/or the calculated values of the pressure gradient are low-pass-filtered.

4. The method as claimed in claim 3, wherein the limit frequency of the low-pass filtering of the pressure values detected by sensor and/or of the calculated values of the pressure gradient lies in the range from 0.1 Hz to 0.3 Hz.

5. The method as claimed in claim 2, wherein the calculated values of the pressure gradient are low-pass-filtered for a set time period after the determination of a pronounced drop in the supply pressure.

6. The method as claimed in claim 1, wherein the comparison of the pressure gradient with the gradient limit value does not take place at positive pressure gradients.

7. The method as claimed in claim 1, wherein the calculation of the values of the pressure gradient or the comparison of the pressure gradient with the gradient limit value is suspended for a set time period after the determination of a pronounced drop in the supply pressure.

8. The method as claimed in claim 1, wherein, during a regeneration operation of the compressed air supply system and/or when a compressed air consumer with permanent compressed air consumption is present, there is used in the comparison of the determined pressure gradient with a gradient limit value instead of the previous gradient limit value a correspondingly reduced gradient limit value.

9. The method as claimed in claim 1, wherein the monitoring time period is defined as the cumulative operating time of the motor vehicle.

10. The method as claimed in claim 1, wherein the monitoring time period is defined as the cumulative distance travelled by the motor vehicle.

11. The method as claimed in claim 1, characterized in wherein the monitoring time period is defined as the cumulative delivery pause of the compressor.

12. The method as claimed in claim 1, wherein a plurality of leakage accounts are kept for different leakage causes, and wherein the gradient limit value and/or the nature and length of the monitoring time period is set differently for the monitoring of different leakage causes.

13. The method as claimed in claim 1, wherein, for the detection of specific leakage causes, the calculation of the values of the pressure gradient is carried out in only a limited range of the supply pressure.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0032] The foregoing aspects and many of the attendant advantages will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts throughout the various views, unless otherwise specified:

[0033] FIG. 1 is a diagram showing the profiles over time of different characteristic values of a compressed air supply system, and

[0034] FIG. 2 shows the schematic construction of a typical compressed air supply system of a motor vehicle, in which the method according to the invention can be carried out.

DETAILED DESCRIPTION

[0035] In FIG. 2, a compressor 2 and an electronically controlled compressed air supply system 4 of a motor vehicle are shown in schematic form, in which the method according to the invention for leakage monitoring of a compressed air system can be used. The compressed air supply system 4 has the assembly groups of a compressed air conditioning unit 6, a multiple-circuit protection valve unit 8 and an electronic control unit 10.

[0036] The compressor 2 is connected on the output side to a delivery line 12 and has a control pressure input 14. By applying a sufficiently high control pressure to the control pressure input 14 from a connected control pressure line 16, a friction coupling, not shown, is engaged, whereby the compressor 2 is connected for drive to a drive motor, not shown, of the motor vehicle and is thereby switched into delivery operation. In delivery operation, the compressor 2 draws in air from the surroundings and delivers it as compressed air into the delivery line 12.

[0037] The compressed air conditioning unit 6 has a dryer line 18 in which there are arranged, in succession in a conveying direction indicated by the direction arrow 42, a filter unit 20, a dryer unit 22 and a non-return valve 24. The dryer line 18 is connected on the input side to the delivery line 12 and branches on the output side into two main supply lines 26, 28. The second main supply line 28 is limited in terms of its maximum pressure by a built-in pressure limiting valve 30. Upstream of the filter unit 20, a vent line 32 branches from the dryer line 18, in which vent line there is arranged a vent valve 34 and which leads via a sound suppressor 36 into the surroundings. The vent valve 34 is in the form of a pressure-controlled 2/2-way changeover valve which is closed in the control-pressureless state and can be opened by the application of a sufficiently high control pressure to a control pressure line 38 connected to its control pressure input. Between the dryer unit 22 and the non-return valve 24, a regeneration line 40 is connected to the dryer line 18.

[0038] The multiple-circuit protection valve unit 8 comprises five overflow valves 46, 50, 54, 58, 62 of a multiple-circuit protection valve, not shown in greater detail, a regeneration control valve 74, a compressor control valve 70 and two throttle-type non-return valves 66, 78. In the multiple-circuit protection valve unit 8, the first main supply line 26 branches into three supply lines 44, 48, 52 of three compressed air consumer circuits V21, V22, V25. The compressed air consumer circuits V21, V22, V25 are, for example, a first service brake circuit of the motor vehicle V21, a second service brake circuit of the motor vehicle V22 and an air suspension circuit V25.

[0039] The pressure-limited second main supply line 28 branches in the multiple-circuit protection valve unit 8 into the two supply lines 56, 60 of two further compressed air consumer circuits V23, V24 and into a control pressure main line 68. The further compressed air consumer circuits V23, V24 are, for example, a trailer and parking brake circuit V23 and an auxiliary consumer circuit V24. One of the overflow valves 46, 50, 54, 58, 62 of the multiple-circuit protection valve is arranged in each of the supply lines 44, 48, 52, 56, 60 of the mentioned compressed air consumer circuits V21, V22, V23, V24, V25. The alternative control pressure main line 68a depicted by a broken line illustrates that the control pressure main line 68 can also branch from the first main supply line 26 between the non-return valve 24 and the pressure limiting valve 30.

[0040] On the output side of the overflow valves 58, 50 in question, a connecting line 64 having the throttle-type non-return valve 66 that opens in the direction of the supply line 48 of the second service brake circuit V22 is arranged between the supply line 56 of the trailer and parking brake circuit V23 and the supply line 48 of the second service brake circuit V22. Via this connection, compressed air can flow in the case of a corresponding pressure gradient from the trailer and parking brake circuit V23 into the second service brake circuit V22 and fill the second service brake circuit, and the trailer and parking brake circuit V23 can be emptied.

[0041] The compressor control valve 70 and the regeneration control valve 74 are connected on the input side to the control pressure main line 68. The two control valves 70, 74 are each in the form of a 3/2-way magnetic switching valve, the connections on the input side of which are blocked in the deenergized state and which are switchable by the energization of an associated electrical control line 72, 76. By energization of the compressor control valve 70, the control pressure line 16 connected to the compressor control valve 70 on the output side is connected to the control pressure main line 68, whereby the friction clutch at the compressor 2 is disengaged and the compressor 2 is uncoupled from the drive motor. When the control pressure input 14 of the compressor 2 is pressureless, the friction clutch of the compressor 2 is engaged, so that the compressor 2 is then in delivery operation when the drive motor is running. In delivery operation, the compressor 2 delivers compressed air, in the delivery direction indicated by the direction arrow 42, through the delivery line 12, the filter unit 20, the dryer line 18, the filter unit 20, the dryer unit 22 and the non-return valve 24 into the two main supply lines 26, 28 and via the overflow valves 46, 50, 54, 58, 62 of the multiple-circuit protection valve further into the mentioned compressed air consumer circuits V21, V22, V23, V24, V25.

[0042] By energization of the regeneration control valve 74, the regeneration line 40 connected on the output side thereto, in which the throttle-type non-return valve 78 that opens in the direction of the dryer line 18 is arranged, is connected to the control pressure main line 68. The control pressure line 38 of the vent valve 34, which is connected to the regeneration line 40 between the regeneration control valve 74 and the throttle-type non-return valve 78, is thereby also subjected to the pressure prevailing in the control pressure main line 68, whereby the vent valve 34 is opened. As a result, already dried compressed air then flows from the second main supply line 28 via the control pressure main line 68 and the regeneration line 40 contrary to the delivery direction 42 through the dryer unit 22 and the filter unit 20 via the vent line 32 and the sound suppressor 36 into the surroundings, whereby the dryer unit 22 is regenerated and the filter unit 20 is cleaned.

[0043] A pressure sensor 82, 88, 94 is connected to the supply lines 44, 48, 56 of the first service brake circuit V21, of the second service brake circuit V22 and of the trailer and parking brake circuit V23 via in each case a connection line 80, 86, 92. The pressure sensors 82, 88, 94 are each connected via an electrical sensor line 84, 90, 96 to an electronic control unit 98 (ECU). The compressor control valve 70 and the regeneration control valve 74 are likewise connected to the electronic control unit 98 for signaling via their electrical control lines 72, 76. The three pressure sensors 82, 88, 94 and the electronic control unit 98 are combined in the assembly group of the electronic control unit 10.

[0044] The method according to the invention for leakage monitoring of a compressed air system will be explained hereinbelow by way of example with reference to the above-described embodiment and arrangement of the compressor 2 and of the compressed air supply system 4 via the diagram of FIG. 1.

[0045] In the diagram, the delivery pressure pF acting at the output of the compressor 2 in the delivery line 12 and the supply pressure pV acting in one of the supply lines 44, 48, 56 and detected via a pressure sensor 82, 88, 94 are shown over time t. The delivery pressure pF of the compressor 2 is not itself detected by sensor and is in the present case contained in the diagram of FIG. 1 only for better understanding. There are further shown in the diagram of FIG. 1 the profiles over time of the low-pass-filtered supply pressure pV_F, of the pressure gradient grd_p.sub.V determined from the values of the low-pass-filtered supply pressure p.sub.V_F, of a gradient limit value grd_p.sub.G and of a gradient limit value grd_p.sub.G-R provided for a regeneration operation of the compressed air supply system 4 and correspondingly reduced.

[0046] The leakage monitoring method provides that the supply pressure p.sub.V in the supply line 44, 48 of at least one compressed air consumer circuit V21, V22 provided with a pressure sensor 82, 88 is continuously detected by sensor in a predefined time interval Δt. The determined pressure values of the supply pressure p.sub.V are then low-pass-filtered with a limit frequency f.sub.G which lies in the range between 0.1 Hz and 0.3 Hz (0.1 Hz≤f.sub.G≤0.3 Hz). At least during the delivery pauses T.sub.FP1, T.sub.FP2, T.sub.FP3of the compressor 2, the pressure gradients grd_p.sub.V of the supply pressure p.sub.V are then continuously calculated from in each case at least two successively detected and low-pass-filtered pressure values p.sub.V_i, p.sub.V+1 and the time difference Δt between the detection thereof.

[0047] These pressure gradients grd_p.sub.V are compared with a predefined gradient limit value grd_p.sub.G which has been determined in a suitable manner beforehand, for example during the development and testing of the motor vehicle in question or the application of the compressed air system in the motor vehicle.

[0048] If the pressure gradient grd_p.sub.V of the low-pass-filtered supply pressure p.sub.V_F has not exceeded the gradient limit value grd_p.sub.G within a predefined monitoring time period T.sub.M, which can be regarded, for example, as the time period illustrated in the diagram of FIG. 1, during the delivery pauses T.sub.FP1, T.sub.FP2, T.sub.FP3 of the compressor 2, a warning signal is outputted.

[0049] The warning signal can be given by the illumination of a warning lamp on the dashboard or on the instrument panel of the motor vehicle, by the illumination of a corresponding warning symbol on the instrument panel, by the display of a corresponding warning text on a display of the instrument panel and/or by the storage of a corresponding fault message in a fault memory associated with the electronic control unit 10 of the compressed air supply system 4.

[0050] The time period TM depicted in the diagram of FIG. 1 comprises three delivery pauses T.sub.FP1, T.sub.FP2, T.sub.FP3 of the compressor 2. Since the pressure gradient grd_p.sub.V of the supply pressure pv has exceeded the predefined gradient limit value grd_p.sub.G in the first delivery pause T.sub.FP1 and in the third delivery pause T.sub.FP3, it is assumed in the present example case that operation is leakage-free and no warning signal is outputted.

[0051] In the delivery pauses T.sub.FP1, T.sub.FP2, T.sub.FP3 there is a larger drop in the supply pressure p.sub.V four times owing to the removal in each case of a larger amount of compressed air in one of the compressed air consumer circuits. In the following time period T.sub.A, thermodynamic effects occur which lead to a pressure increase of the supply pressure p.sub.V. As an alternative to the above-described method with low-pass filtering, the pressure gradient grd_p.sub.V can also be calculated using the supply pressure p.sub.V without low-pass filtering. In order to eliminate the disturbing effect of the rise in pressure, the comparison of the pressure gradient grd_p.sub.V with the gradient limit value grd_p.sub.G is suspended for a previously set time period T.sub.A. Accordingly, only the profile of the pressure gradient grd_p.sub.V without low-pass filtering within the delivery pauses T.sub.FP1, T.sub.FP2, T.sub.FP3 of the compressor 2 outside the time period T.sub.A in question is significant for the detection of a leakage.

[0052] For further illustration, the diagram of FIG. 1 also shows a gradient limit value grd_p.sub.G_R provided for a regeneration operation of the compressed air supply system 4 which here is present at the start of each of the delivery pauses T.sub.FP1, T.sub.FP2, T.sub.FP3, which gradient limit value is correspondingly lowered compared to the gradient limit value grd_p.sub.G applicable for normal operation (grd_p.sub.G_R<grd_p.sub.G). Via the lowered gradient limit value grd_p.sub.G_R, account is taken of the reduction of the supply pressure pv and of the pressure gradient grd_p.sub.V of the supply pressure pv that is caused by the compressed air volume flow removed through the second main supply line 28 for regeneration of the dryer unit 22.

[0053] Within the scope of the monitoring method, a plurality of leakage accounts can be kept for different leakage causes, for which the gradient limit value grd_p.sub.G and/or the nature and length of the monitoring time period TM can be set in different ways. Likewise, in order to detect specific leakage causes, the calculation of the pressure gradient grd_p.sub.V can be carried out in only a limited range of the supply pressure p.sub.V.

[0054] The terms “comprising” or “comprise” are used herein in their broadest sense to mean and encompass the notions of “including,” “include,” “consist(ing) essentially of,” and “consist(ing) of. The use of “for example,” “e.g.,” “such as,” and “including” to list illustrative examples does not limit to only the listed examples. Thus, “for example” or “such as” means “for example, but not limited to” or “such as, but not limited to” and encompasses other similar or equivalent examples. The term “about” as used herein serves to reasonably encompass or describe minor variations in numerical values measured by instrumental analysis or as a result of sample handling. Such minor variations may be in the order of ±0-25, ±0-10, ±0-5, or ±0-2.5, % of the numerical values. Further, The term “about” applies to both numerical values when associated with a range of values. Moreover, the term “about” may apply to numerical values even when not explicitly stated.

[0055] Generally, as used herein a hyphen “-” or dash “—” in a range of values is “to” or “through”; a “>” is “above” or “greater-than”; a “≥” is “at least” or “greater-than or equal to”; a “<” is “below” or “less-than”; and a “≤” is “at most” or “less-than or equal to.” On an individual basis, each of the aforementioned applications for patent, patents, and/or patent application publications, is expressly incorporated herein by reference in its entirety in one or more non-limiting embodiments.

[0056] It is to be understood that the appended claims are not limited to express and particular compounds, compositions, or methods described in the detailed description, which may vary between particular embodiments which fall within the scope of the appended claims. With respect to any Markush groups relied upon herein for describing particular features or aspects of various embodiments, it is to be appreciated that different, special, and/or unexpected results may be obtained from each member of the respective Markush group independent from all other Markush members. Each member of a Markush group may be relied upon individually and or in combination and provides adequate support for specific embodiments within the scope of the appended claims.

[0057] The present invention has been described herein in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. The present invention may be practiced otherwise than as specifically described within the scope of the appended claims. The subject matter of all combinations of independent and dependent claims, both single and multiple dependent, is herein expressly contemplated.

LIST OF REFERENCE SIGNS

[0058] 2 compressor [0059] 4 compressed air supply system [0060] 6 compressed air conditioning unit (assembly group) [0061] 8 multiple-circuit protection valve unit (assembly group) [0062] 10 electronic control unit (assembly group) [0063] 12 delivery line [0064] 14 control pressure input [0065] 16 control pressure line [0066] 18 dryer line [0067] 20 filter unit [0068] 22 dryer unit [0069] 24 non-return valve [0070] 26 first main supply line [0071] 28 second main supply line [0072] 30 pressure limiting valve [0073] 32 vent line [0074] 34 vent valve [0075] 36 sound suppressor [0076] 38 control pressure line [0077] 40 regeneration line [0078] 42 direction arrow, delivery direction [0079] 44 supply line [0080] 46 overflow valve [0081] 48 supply line [0082] 50 overflow valve [0083] 52 supply line [0084] 54 overflow valve [0085] 56 supply line [0086] 58 overflow valve [0087] 60 supply line [0088] 62 overflow valve [0089] 64 connecting line [0090] 66 throttle-type non-return valve [0091] 68 control pressure main line [0092] 68a alternative control pressure main line [0093] 70 compressor control valve [0094] 72 electrical control line [0095] 74 regeneration control valve [0096] 76 electrical control line [0097] 78 throttle-type non-return valve [0098] 80 connection line [0099] 82 pressure sensor [0100] 84 electrical sensor line [0101] 86 connection line [0102] 88 pressure sensor [0103] 90 electrical sensor line [0104] 92 connection line [0105] 94 pressure sensor [0106] 96 electrical sensor line [0107] 98 electronic control unit (ECU) [0108] f.sub.G limit frequency [0109] grd_p pressure gradient (general) [0110] grd_p.sub.G gradient limit value [0111] grd_p.sub.G_R reduced gradient limit value [0112] grd_p.sub.V pressure gradient of the supply pressure [0113] p pressure (general) [0114] p.sub.F delivery pressure of the compressor [0115] p.sub.V supply pressure [0116] p.sub.V_F low-pass-filtered supply pressure [0117] p.sub.V_i i.sup.th measured value of the supply pressure [0118] p.sub.V_i+1 (i+1).sup.th measured value of the supply pressure [0119] t time [0120] T.sub.A time period [0121] T.sub.M monitoring time period [0122] T.sub.F1 first delivery operation duration [0123] T.sub.F2 second delivery operation duration [0124] T.sub.F3 third delivery operation duration [0125] T.sub.F4 fourth delivery operation duration [0126] T.sub.FP1 first delivery pause [0127] T.sub.FP2 second delivery pause [0128] T.sub.FP3 third delivery pause [0129] V21 compressed air consumer circuit, first service brake circuit [0130] V22 compressed air consumer circuit, second service brake circuit [0131] V23 compressed air consumer circuit, trailer and parking brake circuit [0132] V24 compressed air consumer circuit, auxiliary consumer circuit [0133] V25 compressed air consumer circuit, air suspension circuit [0134] Δt time interval, time difference