Method and device for detecting a fault in an air supply system

Abstract

In a method for detecting a change, in particular a degradation, in the delivery capacity of a compressor of an air supply system of a motor vehicle, a maximum lift-off duration for a certain lift-off distance or a pressure increase to be achieved at least after a certain operating duration of the compressor is determined for a previously determined ambient pressure according to a characteristic curve. If the lift-off duration is longer than a corresponding value determined according to the characteristic curve or the pressure increase is less than a corresponding value determined according to the characteristic curve, a fault signal is output.

Description

Technical Field

[0001] The present invention relates to a vehicle chassis, and in particular to an air spring system of a vehicle chassis. Background Art

[0002] In addition to motor vehicles, air suspensions are also used in passenger vehicles of premium equipment, where they are particularly appreciated for their particularly fine response behavior and the possibility of height adjustment.

[0003] Air spring systems for vehicles usually include an air spring at each end of each axle, which is loaded with compressed air at the corresponding required pressure by means of a compressor. The individual control of the individual air springs can be achieved by means of corresponding valves, such as solenoid valves. In order to be able to change the pressure particularly quickly when necessary, an accumulator is usually provided in the air spring system, in which high-pressure air is stored. Therefore, when a higher pressure is suddenly required in the air spring, this higher pressure can be provided more quickly than if it has to be generated for a short time by means of a compressor.

[0004] Air springs in road vehicles are constructed in two forms: one form is an air spring with a constant volume in the controlled position, and the other form is a gas spring with a constant amount of gas.

[0005] In a first embodiment, the air is enclosed in a gas-tight, variable volume, for example in a cylinder with a piston that can move therein or in a rolling bellows. The air spring is supplied with compressed air by a compressor. Depending on the load, the air is pumped in or out, that is, the pressure in the volume is increased or decreased, so that the filling volume and thus the horizontal attitude of the vehicle remain constant. In order to ensure a certain spring action in the event of failure of the air suspension, an emergency spring, for example a rubber spring, can be provided. In the normal attitude, the pressure level is about 5 to 12 bar, in the case of dynamic contraction, the pressure can be about 10 to 20 bar, depending on the load.

[0006] In the second construction form, a certain amount of gas is enclosed in the spring element. As the load increases, the volume decreases and the suspension becomes stiffer. Level compensation is achieved by means of an additional hydraulic system. This construction form is known, for example, as a hydropneumatic device in Citroën brand vehicles.

[0007] Compared to metallic springs, air springs generally have the advantage of a finer response, since air has almost no inherent damping. Furthermore, as mentioned above, in the case of the first design of air springs, the preload force, by means of which the vehicle height can be set, can be set to a certain extent by setting a specific pressure. By automatically setting the preload force, the vehicle height can be maintained independently of the load, i.e., automatic leveling can be achieved.

[0008] In chassis with air springs of the first design (i.e. air springs with a constant volume in the controlled attitude), it is essential that the compressor can always provide the required minimum pressure in order to ensure a correspondingly correct setting of the air spring system in any driving situation and chassis setting. In addition, there are only slight leaks in the compressed air lines and connections (if any) so that the pressure in the system does not drop uncontrollably.

[0009] In order to identify a defective air supply system, the delivery capacity is monitored in known air supply systems for motor vehicles. This can be done by monitoring the time required to raise the vehicle body to a certain height. It should be noted that since the air pressure decreases with increasing altitude above the normal altitude zero point (i.e. the long-term average value at sea level), the delivery capacity of the compressor decreases correspondingly continuously. Thus, at an altitude of 1000 m above sea level, the air pressure is only about 88% of the pressure at sea level; at an altitude of 2000 m above sea level, the air pressure is only about 77%, and at an altitude of 3000 m, the air pressure is only about 68%.

[0010] Here, for example, the lower limit of the delivery capacity can be determined in such a way that the vehicle body is still lifted to a certain extent within the maximum permissible duration or "lift time" under the most unfavorable possible conditions. The "most unfavorable conditions" are determined by the maximum permissible total weight of the vehicle, a compressor that is just at the lower limit of the permissible tolerance of the delivery capacity, and a maximum operating altitude above the normal altitude zero point (i.e., the maximum altitude above the normal altitude zero point at which the vehicle is to be operated). The air pressure that prevails at the maximum operating altitude can be achieved by actual operation at this altitude or in the pressure chamber. The remaining parameters can be easily set at any position.

[0011] If the maximum permissible lifting time or filling time of the pressure accumulator is exceeded during normal operation, the air supply device is detected as defective. In addition, in the event of a defect, the maximum pressure accumulator filling threshold is reduced to avoid long-term continuous operation of the compressor. The compressor is correspondingly operated more frequently for shorter time spans to avoid compressor overheating. In previous methods, it is not possible to detect a deterioration in the delivery performance of the compressor at an early stage. Since the most unfavorable conditions are usually rarely present during operation, it may happen that a defect is detected when the air supply device could have been classified as defective long ago under the most unfavorable conditions in actual operation.

[0012] The object of the present invention is to specify a method and a device for monitoring an air supply system, which method allows early detection of changes, in particular degradation, in the delivery capacity of a compressor of the air supply system. Summary of the invention

[0013] This object is achieved by the method described in item 1 below and the device described in item 5 below. Advantageous embodiments and improvements are described in the corresponding other items.

[0014] 1. A method for detecting a change in the delivery capacity of a compressor of an air supply system of a motor vehicle, wherein the air supply system comprises a pressure accumulator and at least one pressure line to an air spring, the pressure lines being connected, like the compressor, to a pressure distribution rail connected to a pressure sensor via a valve controllable by a control device of the air supply system, wherein the method comprises:

[0015] - closing the controllable valves to the air spring, the compressor and the pressure accumulator,

[0016] - venting the pressure distribution rail to the ambient atmosphere,

[0017] - measuring the ambient pressure in the pressure distribution rail after the exhaust gas by means of the pressure sensor and at least temporarily storing the measured ambient pressure,

[0018] - operating the compressor for a predetermined period of time, or raising the motor vehicle by means of the at least one air spring over a specific distance,

[0019] - measuring the pressure developed in the pressure distribution rail due to the operation of the compressor, or measuring the time required for lifting a certain distance,

[0020] - comparing the measured pressure that develops in the pressure distribution rail due to the operation of the compressor or the measured time with a value of a characteristic curve read out from a memory, which value corresponds to a minimum pressure in the pressure distribution rail to be expected during the operating time of the compressor at the measured ambient pressure or to a maximum permissible lift time for a specific distance at the measured ambient pressure, and

[0021] If the measured pressure resulting from the operation of the compressor is lower than the pressure read out from the memory or the rise time is longer than the rise time read out from the memory, a signal representing a fault is output.

[0022] 2. The method according to the preceding item 1, wherein venting the pressure distribution rail to the ambient atmosphere comprises opening the valve via which the compressor is connected to the pressure distribution rail, wherein the compressor is not running.

[0023] 3. The method according to item 1 or 2 above, wherein the method is performed periodically at predetermined time intervals or after a trigger signal.

[0024] 4. A method according to any one of items 1 to 3 above, wherein after each implementation of the method, a value representing the delivery power of the compressor is determined and stored, and a trend is determined based on the stored multiple values ​​representing the delivery power of the compressor, and a time point at which the delivery power of the compressor is likely to no longer meet the minimum requirement is determined based on the trend.

[0025] 5. A control device for an air supply device of a motor vehicle, the control device having a microprocessor, a volatile memory and a non-volatile memory, and one or more control outputs for controlling a valve or one or more sensor inputs for acquiring sensor measurement values, wherein the non-volatile memory stores computer program instructions in a callable manner, and when the computer program instructions are implemented in the volatile memory by the microprocessor, the control device is configured to control the air supply device to implement a method according to any one of items 1 to 4 above.

[0026] 6. An air supply device for an air spring system of a vehicle, the air supply device having a compressor, a pressure accumulator and at least one pressure line leading to an air spring, each of the pressure lines being connected to a pressure distribution rail connected to a pressure sensor via a valve that can be controlled by a control device, wherein the air supply device includes a control device according to item 5 above and is configured to implement a method according to any one of items 1 to 4 above.

[0027] 7. A motor vehicle having a chassis with air springs and an air supply device according to item 6, the control device of which is configured for implementing the method according to one or more of items 1 to 4.

[0028] 8. A computer program product comprising instructions, which, when the program is executed by a computer, cause the computer to control an air supply device connected to a control output and a signal input of the computer to perform the method according to one or more of the above items 1 to 4.

[0029] 9. A computer-readable medium, on which the computer program product according to item 8 above is stored.

[0030] To achieve this purpose, a method for identifying a change, in particular a degradation, in the delivery power of a compressor of an air supply device of a motor vehicle is proposed. In addition to the compressor, the air supply device also includes a control device and a pressure accumulator. The compressor, the pressure accumulator and at least one air spring are each connected to a pressure distribution rail connected to a pressure sensor via a pressure line and a valve controllable by the control device. The method first comprises: closing the controllable valves of all components connected to the pressure distribution rail of the air supply device (if these valves are not already closed). Subsequently, the pressure distribution rail is vented to the surrounding atmosphere, for example by opening a vent valve provided for this purpose or by opening a controllable valve, via which the compressor is connected to the pressure distribution rail, wherein the compressor is not running. Therefore, in a second alternative, the pressure distribution rail is vented to the ambient atmosphere via the compressor. The pressure in the pressure distribution rail is now measured using a pressure sensor connected to the pressure distribution rail, which now corresponds to the air pressure of the ambient atmosphere. Subsequently, the compressor is operated for a predetermined period of time, and the pressure formed in the pressure distribution rail due to the operation of the compressor is measured again. The pressure formed after the compressor is running can be compared with the value stored in the characteristic curve for the previously measured ambient pressure, which represents the pressure that must be reached at least for the ambient pressure and the operating time of the compressor. If the minimum pressure is not reached, a signal representing a fault is output. Alternatively, the vehicle body can be raised a specific distance by means of air suspension after measuring the ambient pressure, and the time required for the lifting can be measured. This time can then be compared with the value stored in the characteristic curve for the previously measured ambient pressure, which represents the maximum time allowed for the ambient pressure and the specific distance. In another alternative, the gradient of the pressure increase or the delivery power during the operation of the compressor is determined and compared with the value read from the characteristic curve for the previously determined ambient pressure. Therefore, in the method according to the invention, the actual delivery power of the compressor is compared with the minimum rated delivery power at the corresponding ambient pressure.

[0031] In all alternatives, a lower maximum pressure in the pressure accumulator can be associated with a lower ambient pressure, whereby unnecessarily long operating times of the compressor can be avoided.

[0032] All alternatives of the method according to the invention allow a drop in the delivery capacity of the compressor of the air supply system below a specified minimum value to be detected already at an early stage (such a drop would otherwise only be detectable during operation under the most unfavorable conditions) in order to indicate such a drop in the delivery capacity in a timely manner.

[0033] The method can be carried out periodically at predetermined time intervals in order to detect a gradual change in the delivery capacity of the compressor. However, the method can also be carried out in response to a trigger signal. For example, a corresponding trigger signal can be generated each time the vehicle is started or each time the compressor starts operating in order to refill the pressure accumulator.

[0034] In one or more embodiments of the method, each time the method is carried out, a value representing the delivery power of the compressor is determined and stored, for example, in a control device of the air supply system. Preferably, the time at which the method is carried out is also stored. A trend can be determined based on the stored multiple values ​​representing the delivery power of the compressor. Based on the trend, a time can be determined at which the delivery power of the compressor no longer meets the minimum requirement with a high probability. The determined time can be indicated to the user of the vehicle so that repairs or maintenance can be planned in a timely manner.

[0035] The control device according to the invention for an air supply system of a motor vehicle comprises a microprocessor, a volatile memory and a non-volatile memory and one or more control outputs for actuating valves or one or more sensor inputs for acquiring sensor measured values ​​(e.g., pressure measured values ​​or the lift height of the vehicle body), which are communicatively connected to one another via one or more data lines or data buses. The non-volatile memory stores computer program instructions that can be called up therefrom, and when the microprocessor executes the computer program instructions in the volatile memory, the control device is configured to actuate the air supply system to implement one or more embodiments of the method according to the invention.

[0036] The air supply device according to the invention for an air spring system of a vehicle comprises a compressor, a pressure accumulator and at least one pressure line leading to an air spring. The compressor, the pressure accumulator and the at least one pressure line are connected to a pressure distribution rail connected to a pressure sensor via a valve controllable by a control device according to the invention. The control device according to the invention is configured to control the air supply device to carry out one or more embodiments of the method according to the invention.

[0037] A computer program product for implementing the method according to the invention contains instructions which, when executed by a computer, cause the computer to control an air supply device connected to the control outputs and signal inputs of the computer to carry out one or more embodiments and refinements of the method described above.

[0038] The computer program product may be stored on a computer-readable medium or data carrier. The medium or data carrier may be physically materialized, such as a hard disk, CD, DVD, flash memory, etc., but the medium or data carrier may also include a modulated electrical signal, electromagnetic signal or optical signal, which can be received by a computer with the aid of a corresponding receiver and stored in a memory of the computer. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The present invention is described below with reference to the accompanying drawings. In the accompanying drawings:

[0040] Figure 1 A schematic block diagram shows an exemplary air supply device according to the invention for a motor vehicle and an air spring connected thereto,

[0041] Figure 2 A flow chart showing an exemplary method according to the invention for detecting a change in the delivery capacity of a compressor of an air supply system of a motor vehicle, and

[0042] Figure 3 A schematic block diagram of an exemplary control device for carrying out the method according to the present invention is shown.

[0043] In the drawings, identical or similar elements are referenced by identical reference numerals. DETAILED DESCRIPTION

[0044] Figure 1 A schematic block diagram of an exemplary air supply device 200 according to the present invention of a motor vehicle and air springs 208-1, 208-2, 208-3, 208-4 connected thereto is shown. The components of the air supply device 200 are arranged in a rectangle drawn with dashed lines. The compressor 202 is connected to a pressure distribution rail 216 via a controllable valve 212-5, and a pressure sensor 214 is also connected to the pressure distribution rail. Pressure lines 210-1, 210-2, 210-3 and 210-4 start from the pressure distribution rail 216 and reach air springs 208-1, 208-2, 208-3 and 208-4 via controllable valves 212-1, 212-3, 212-4 and 212-6. The pressure accumulator 206 is connected to the pressure distribution rail 216 via a controllable valve 212-2. The control device 204 is connected to controllable valves 212 - 1 , 212 - 2 , 212 - 3 , 212 - 4 , 212 - 5 and 212 - 6 , the compressor 202 and the pressure sensor 214 via sensor lines and control lines (not shown in detail).

[0045] Figure 2 A flow chart showing an exemplary method 100 according to the present invention for identifying a reference of a motor vehicle Figure 1Change of the delivery capacity of the compressor 202 of the air supply device 200 described by way of example. In step 102, if the controllable valve is not closed yet, the controllable valves 212-1, 212-2, 212-3, 212-4, 212-5 and 212-6 are closed. In step 104, the pressure distribution rail 216 is vented toward the ambient atmosphere, for example by opening the vent valve provided for this purpose or by opening the valve 212-5 leading to the compressor 202, while the compressor is not running at this time. In step 106, the ambient pressure in the pressure distribution rail 216, which is now vented and in fluid connection with the environment, is measured and at least temporarily stored. In the next step 108, the compressor 202 is operated for a predetermined time period, or alternatively the motor vehicle is lifted by means of at least one air spring for a specific distance. Subsequently, in step 110, the pressure formed in the pressure distribution rail 216 due to the operation of the compressor 202 is measured or the time required for lifting the vehicle for a specific distance is measured. In step 112, the pressure that is built up in the pressure distribution rail 216 due to the operation of the compressor 202 is compared with a value read from a characteristic curve, which corresponds to the minimum pressure in the pressure distribution rail 216 that is expected during the operating time at the previously measured ambient pressure. If, alternatively, a time is measured for lifting the vehicle over a certain distance, this time is compared with a value read from a characteristic curve, which corresponds to the maximum permissible lifting time for a certain distance at the measured ambient pressure. If the minimum pressure has been reached or exceeded, or if the maximum permissible lifting time has been exceeded, i.e. the "ja (yes)" branch of step 112, the method is terminated. Otherwise, i.e. the "nein (no)" branch of step 112, a signal is output in step 114 that signals a fault and, if necessary, is stored in a fault memory before the method is terminated. In this case, the operating time and the pressure increase achieved or the time required for lifting the vehicle can optionally be stored together with the ambient pressure in step 116 before termination for further evaluation.

[0046] Figure 3 A schematic block diagram of an exemplary control device 204 for executing the method 100 according to the present invention is shown. A microprocessor 2042, a volatile memory 2044, a non-volatile memory 2046 and a control output or a sensor input 2048 are communicatively connected to one another via one or more data lines or a data bus 2050. The non-volatile memory 2046 contains computer program instructions, which, when executed by the microprocessor 2042 in the volatile memory 2044, the control device 204 is configured to implement an air supply device to implement one or more embodiments of the method according to the present invention.

Claims

1. A method (100) for detecting a change in the delivery capacity of a compressor (202) of an air supply device (200) of a motor vehicle, wherein the air supply device (200) comprises a pressure accumulator (206) and at least one pressure line (210-1, 210-2, 210-3, 210-4) leading to an air spring (208-1, 208-2, 208-3, 208-4), the pressure line and the compressor (202) each being connected to a pressure distribution rail (216) connected to a pressure sensor (214) via a valve (212-1, 212-2, 212-3, 212-4, 212-5, 212-6) controllable by a control device (204) of the air supply device (200), wherein the method (100) comprises: - closing (102) the controllable valves (212-1, 212-2, 212-3, 212-4, 212-5, 212-6) to the air springs (208-1, 208-2, 208-3, 208-4), the compressor (202) and the pressure accumulator (206), - exhausting (104) the pressure distribution rail (216) to the ambient atmosphere, - measuring (106) the ambient pressure in the pressure distribution rail (216) after venting by means of the pressure sensor (214) and at least temporarily storing the measured ambient pressure, - operating (108) the compressor (202) for a predetermined period of time, or raising the motor vehicle by means of the at least one air spring (208-1, 208-2, 208-3, 208-4) a specific distance, - measuring (110) the pressure developed in the pressure distribution rail (216) due to the operation of the compressor (202), or measuring the time required for lifting a certain distance, - comparing (112) the measured pressure that develops in the pressure distribution rail (216) due to the operation of the compressor (202) or the measured time with a value of a characteristic curve read out from a memory (2046), the value corresponding to the minimum pressure in the pressure distribution rail (216) to be expected during the operating time of the compressor (202) at the measured ambient pressure or to the maximum permissible lifting time for a specific distance at the measured ambient pressure, and - If the measured pressure resulting from the operation of the compressor (202) is less than the pressure read from the memory (2046) or the rise time is longer than the rise time read from the memory, a signal representing a fault is output (114).

2. The method (100) of claim 1, wherein venting (104) the pressure distribution rail (216) to ambient atmosphere comprises opening the valve (212-5), the compressor (202) being connected to the pressure distribution rail (216) via the valve, wherein the compressor (202) is not operating.

3. The method (100) according to claim 1 or 2, wherein the method is performed periodically at predetermined time intervals or after a trigger signal.

4. A method (100) according to claim 1 or 2, wherein after each implementation of the method, a value representing the delivery power of the compressor (202) is determined and stored, and a trend is determined based on the stored multiple values ​​representing the delivery power of the compressor (202), and the time point at which the delivery power of the compressor (202) no longer meets the minimum requirement is determined based on the trend.

5. A control device (204) of an air supply device (200) of a motor vehicle, the control device having a microprocessor (2042), a volatile memory (2044) and a non-volatile memory (2046) and one or more control outputs (2048) for controlling valves (212-1, 212-2, 212-3, 212-4, 212-5, 212-6) or one or more sensor inputs (2048) for acquiring sensor measurement values, wherein the non-volatile memory (2046) stores computer program instructions in a callable manner, and when the computer program instructions are executed by the microprocessor (2042) in the volatile memory (2044), the control device (204) is configured to control the air supply device (200) to implement the method according to any one of claims 1 to 4.

6. An air supply device (200) for an air spring system of a vehicle, the air supply device having a compressor (202), a pressure accumulator (206) and at least one pressure line (210-1, 210-2, 210-3, 210-4) leading to an air spring (208-1, 208-2, 208-3, 208-4), each of the pressure lines being connected to a pressure distribution rail (216) connected to a pressure sensor (214) via a valve (212-1, 212-2, 212-3, 212-4, 212-5, 212-6) controllable by a control device (204), wherein the air supply device (200) includes a control device (204) according to claim 5 and is configured to implement a method according to any one of claims 1 to 4.

7. A motor vehicle having a chassis with air springs (208-1, 208-2, 208-3, 208-4) and an air supply device (200) according to claim 6, the control device (204) of the air supply device being configured for implementing the method (100) according to any one of claims 1 to 4.

8. A computer program product comprising instructions which, when executed by a computer, cause the computer to control an air supply device (200) connected to a control output and a signal input of the computer to perform the method according to any one of claims 1 to 4.

9. A computer-readable medium having stored thereon the computer program product according to claim 8.

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