METHOD AND ARRANGEMENT FOR MEASURING THE PRESSURE IN A COMPRESSED AIR SYSTEM FOR A HEAVY MOTOR VEHICLE

Abstract: A method and an arrangement for measuring the pressure in a compressed air system (1) for a heavy vehicle, whereby the compressed air system incorporates an engine-driven compressor (2) and at least one compressed air circuit (5-8) with compressed air line and consumer. Shutdown of the vehicle's engine initiates measuring (21) of the pressure in each compressed air circuit (5-8) as a function of time, and recording (25) of the resulting measured values. Any leakage in the circuit can thus be monitored. The invention also relates to a compressed air system which includes such an arrangement.

Description: Method and arrangement for measuring the pressure in a compressed air system for a heavy motor vehicle TECHNICAL FIELD 5 The present invention relates to a method and an arrangement for pressure measurement in a compressed air system for a heavy vehicle in accordance with the preamble to patent claims 1 and 8 respectively. 10 STATE OF THE ART A compressed air system for a heavy vehicle includes a compressed air compressor, a compressed air accumulator, a distributor, usually in the form of a distributor valve, and a number of compressed air circuits connected to the distributor valve. Examples of the 15 circuits concerned included compressed air circuits for front brakes, for rear brakes, for trailer brakes, for accessories and for suspension etc. In each circuit, there are also control devices, operating devices etc. for performing the particular function. Considerable leakage problems occur in parts of the system, particularly in older vehicles. 0 Such leakage may cause the compressed air system, after a period of standstill, to be completely empty of compressed air, which means that the compressor has to be run for a certain time to build up the system pressure again. This entails an undesirable loss of time at substantially every start-up of the vehicle, particularly when starting up after it has been at standstill for a prolonged period, such as overnight. Leakage also increases 5 compressor wear and the risk of jeopardising important functions of the vehicle. Checking the tightness of heavy vehicle compressed air systems has previously been conducted when the vehicle is having workshop attention, by measuring the pressure continuously for a certain specified period of time to make it possible to form a picture of 30 pressure changes and hence detect the occurrence of any leakage in the various parts of the system. However, this method is very time-consuming and inefficient and entails an extra cost during vehicle servicing. OBJECTS AND MOST IMPORTANT CHARACTERISTICS OF THE INVENTION One object of the present invention is to indicate a method and an arrangement for measurement of the kind mentioned in the introduction which obviate the disadvantages of the state of the art and provide reliable tightness monitoring without involving specific extra time and consequent costs. These objects are achieved by the features in the characterising parts of patent claims 1 and 8 respectively. Hereby is achieved that a recording of the pressure in each compressed air circuit as a function of time is provided, when the vehicle's engine shuts down, e.g. on the occasion of parking, overnighting etc. This results in several advantages, such as pressures being recorded regularly, creating the possibility of continuous follow-up of pressure changes to enable subsequent assessment of the tightness of the system and particularly of the various compressed air circuits. This means that incipient leakage or degradation of the system can be reliably detected so that leakage can be dealt with at an early stage. For economic reasons it is very important that the servicing and repair of heavy commercial vehicles should as far as possible take place on the occasion of ordinary servicing. The invention creates the possibility of regularly providing a basis for servicing decisions so that this important requirement can be met through the possibility of early detection of incipient degradation of one or more circuits of the compressed air system. It is thus more likely that any compressed air system repairs arising can be done on the occasion of ordinary servicing, thereby making it possible to minimise the need for servicing between such ordinary servicing occasions and the associated unscheduled standstills and extra costs. Comparing measured pressure values with permissible values as a function of time provides the possibility of automatic evaluation of deviations, thus creating a more reliable basis for decisions. This applies particularly if values stored in a reference memory are used so that the vehicle driver's attention can be drawn to incipient degradation of any circuit. At the same time, the permissible values may possibly be at various levels, e.g. an "attention level", a "warning level" and a "servicing level". Inter alia, this can be arranged when setting a reference memory. Comparisons between current pressure values in different circuits can be used to draw attention if the values for a given circuit deviate in such a way that there is probably leakage in that specific circuit. Generating a control signal when deviations exceed a certain level provides the possibility of making the vehicle driver aware that the leakage is abnormal. It also makes it possible to use the control signal for shutting down a circuit affected by detected impermissible leakage. According to a preferred embodiment, measured values are stored in a measured- value memory in which values are available either directly via on-board equipment such as a display, a printer or the like or via externally connectable equipment. It should be emphasised that the term "measured-value memory" is not limitative but that various kinds of both directly received and processed values describing the pressure or pressure change in the particular circuit as a function of time may arise. BRIEF DESCRJP TION OF DRAWINGS Further advantages achieved with the invention are indicated by the ensuing detailed description with reference to the attached drawings, in which: Fig. 1 depicts schematically a compressed air system incorporating an arrangement for pressure measurement according to the invention, and Fig. 2 depicts a flowchart of a method for pressure measurement according to the invention. DESCRIPTION OF EMBODIMENTS Fig. 1 depicts a compressed air system, designated generally by ref. 1, for a commercial vehicle and including a compressed air compressor 2, an accumulator tank 3 and a distributor valve 4. The distributor valve 4 in this embodiment is a circuit protection valve which includes a protective function whereby pressure loss in a circuit can cause shutdown of that valve relative to the remainder of the compressed air system, provided that the circuit concerned is not vital for the operation of the vehicle, in which case the whole operation of the vehicle would have to come to a halt. Using a circuit protection valve thus prevents pressure loss in the other circuits of the system. A number of (here four) compressed air circuits 5 - 8 are connected to the distributor valve 4. The circuits cater for particular equipment items, where there may be a number from the group: one circuit for front brakes, one for rear brakes, one for trailer brakes, one for suspension, one for extra equipment and so on. In each circuit, there are control arrangements and operating arrangements in a conventional manner. In each circuit there is a pressure sensor 9 - 12 connected to a control unit 13. The control unit thus receives signals from the pressure sensors 9 - 12. Also connected to the control unit 13 is a reference memory 14 for storing the set- values for the pressure in the respective circuits as a function of time or, to put it more simply, the permissible values for said pressures. Ref. 15 denotes a measured-value memory designed to store values representing the pressure as a function of time in the respective circuits. The measured- value memory 15 has connected to it an interface to make it possible to connect external equipment, e.g. for indicating or displaying measured-value data. This interface is denoted by ref. 16 and may of course be associated instead with the control unit 13. A signalling unit 17 is connected to the control unit 13. The signalling unit 17 generates an attention signal when impermissible leakage is observed in any of the circuits 5 - 8. This may be a light signal of any kind or an acoustic signal. Fig. 2 is intended to illustrate a method sequence according to the invention whereby ref. 20 denotes the start of the sequence, which is initiated by, for example, the vehicle engine has been shut down or alternatively shutting down the engine for the nt time, meaning that the sequence starts after n shutdowns of the engine. In this connection, n is an integer, e.g. four. In this example the measuring sequence would thus be initiated every fourth time the engine is shut down. Ref. 21 denotes the pressure in the circuits being measured as a function of time, and signals indicating the measured results being generated. Ref. 22 denotes "permissible values" stored in the reference memory being retrieved and led to a comparator. Ref. 23 denotes measured values being compared with said stored permissible values to ascertain the magnitude of the deviation between them. Ref. 24 denotes a control signal being generated if the deviation exceeds a predetermined level. This control signal may for example be led to devices for shutting down a particular compressed air circuit. Ref. 25 denotes display of measured values, which in its simplest form may be by means of lamps such as LEDs but may also be on a display or by printout of curves or discrete values representing pressures as a function of time, possibly with stored reference values intended as stored permissible values. Ref. 26 denotes the end of the sequence. The invention may be varied within the scope of the claims and, for example, the control system may do comparisons between current values for the various circuits to see whether any circuit is deviating from the other circuits with regard to leakage. Measured results may thus be stored so as to be available in the form of a constantly updated measurement record, and there may also be circuits for evaluating changes in leakage over time for the various circuits. Analysis of measured results may be done continuously or upon request. Analysis may take place on board the vehicle or when the vehicle visits a workshop. The combination of not only using reference values but also comparing current values for the various circuits makes it possible to improve redundancy and prevent incorrect indications. Each circuit may also incorporate more than one pressure sensor. Pressures may be measured continuously or at specified intervals of time.

Claims: Patent claims: 1. A method for measuring the pressure in a compressed air system (1) for a heavy vehicle, whereby the compressed air system includes an engine-driven compressor (2) and at least one compressed air circuit (5-8) with compressed air line and consumer, characterised by, when shutting down the vehicle's engine, initiating measuring (21) of the pressure in each compressed air circuit (5-8) as a function of time, and recording (25) of the resulting measured values. 2. A method according to claim 1, characterised in that measured values are compared (23) with permissible values for the pressure as a function of time to detect any deviations due to leakage in the circuit. 3. A method according to claim 2, characterised in that values stored in a reference memory (14) are used as permissible values. 4. A method according to claim 2 or 3, characterised in that current values for the pressure as a function of time for a given circuit or circuits in the system are used as permissible values. 5. A method according to any one of claims 2 - 4, characterised in that a control signal is generated (24) upon deviations exceeding a certain level. 6. A method according to claim 5, characterised in that the control signal is used for shutting down the circuit concerned. 7. A method according to any one of claims 1 - 6, characterised in that measured values are stored in a measured-value memory (15). 8. An arrangement for measuring the pressure in a compressed air system (1) for a heavy vehicle, whereby the compressed air system comprises an engine-driven compressor (2) and at least one compressed air circuit (5-8) with compressed air line and consumer, characterised by initiating means (13) for initiating, when the vehicle's engine shuts 5 down, pressure measurement in each compressed air circuit as a function of time, and by recording means (15) for recording the resulting measured values. 9. An arrangement according to claim 8, characterised by a comparator (13) for comparing measured values for the pressure with permissible values as a function of time 10 in order to determine any deviations due to leakage in the circuit. 10. An arrangement according to claim 9, characterised by a signal emitter (13) for indicating deviations exceeding a certain level. 15 11. An arrangement according to claim 9 or 10, characterised by a reference memory (14) for storing permissible values for the pressure as a function of time. 12. An arrangement according to claim 9 or 10, characterised in that current values denoting the change in pressure as a function of time for a given circuit or circuits of the 20 system arranged to be used by the comparator are used as permissible values. 13. An arrangement according to any one of claims 9 - 12, characterised in that the signal emitter (13) is arranged to generate a control signal for shutting down the circuit concerned (5-8) upon deviations exceeding a certain level. 25 14. An arrangement according to any one of claims 8 - 13, characterised by a measured- value memory (15) for continuous storage of measured values. 15. Compressed air system for a commercial vehicle including an arrangement according 30 to any one of claims 8 - 14.

Inventors: BERGQVIST OLA, BERGQVIST, OLA
Applicants: SCANIA CV ABP, SCANIA CV AB (PUBL)
Application year: 2001
Main classification: G01M3
IPC codes: B60T17, G01M3