Patent Publication Number: US-2009232668-A1

Title: Vehicle including compressed air consuming devices and a method of operating the same

Description:
BACKGROUND AND SUMMARY 
     The present invention relates to a method of operating compressed air systems in vehicles, such as lorries with or without trailers, buses and other heavy vehicles, which include compressed air consuming devices, such as pneumatic braking and suspension systems. 
     Compressed air systems for such vehicles conventionally comprise a power driven compressor to deliver compressed air to one or more storage tanks from which the air consuming devices are fed. The operation of the compressor is usually controlled by a pressure regulator system maintaining an air pressure within the storage tanks at a rather high level, such as about 10-12 bars, which is considered to be sufficient to meet the need of operating the air consuming devices even in the most demanding situations, such as frequent braking or braking over a prolonged period of time. 
     The constant use of such high pressure in the storage tank(s) involves several disadvantages. As the compressor&#39;s efficiency is lower at higher pressure the energy (fuel) consumption for producing pressurised air will increase. Also the oil carry-over from the lubricating system tends to increase with higher pressure as the temperature inside the compressor rises. The increased temperature also makes the oil carry-over more aggressive to gaskets and sealings in the compressed air system. 
     An aspect of the present invention is based on the finding that the high air pressure conventionally used is necessary only in foreseeable or extreme cases, and that a substantially lower pressure is sufficient during a major part of the time in which the vehicle is in use. 
     Thus, an aspect of the present invention provides a method of operating a vehicle system including compressed air consuming devices, said method comprising operating a power driven compressor so as to deliver compressed air to at least one storage tank and so as to maintain the air pressure in the tank substantially at a predetermined first elevated level and selectively supplying compressed air from the compressed air storage tank to any of said devices in order to operate the same, and the method according to an aspect of the invention is characterised in controlling the operation of the compressor by position identification means so as to change the pressure of the air in the storage tank to a predetermined second elevated level or substantially different from said first level in response to receiving from the position identification means an indication to the effect that the vehicle is approaching or has arrived at one of a plurality of predetermined positions and/or positions fulfilling predetermined criteria. 
     Said first air pressure level of the storage tank may, for example, be a minimum value or range between two levels and said second elevated level may be a higher value or range between two levels, the operation of the compressor being controlled so as to change the pressure of the air in the storage tank to said second higher value, when the position identification means identifies positions where an increased consumption of compressed air may be foreseen. Thus, said first pressure level may be a minimum pressure level used under normal operating conditions when no excessive consumption of pressurised air by the air consuming devices is expected or foreseen, and said second pressure level may be a higher pressure level enabling the storage tank to deliver the amount of pressurised air required under special conditions at which frequent and/or prolonged operation of one or more of the air consuming devices is expected. As an example the first pressure level may be in the order of 8 bars and the second pressure level may be around 12 bars. 
     The air pressure system on a truck is sometimes divided in different circuits with different air pressure requirements. This is the case when different air components require different maximum air pressure levels. For example, the braking system requires approximately 8 bars as a maximum pressure level and the air suspension system requires approximately 12 bars as a maximum level. For an unloaded truck, the air suspension pressure may be only 2 bars. When the air suspension does not require a higher pressure level, e.g. when the truck is driven unloaded on a road, there is no need for the air system of the truck to provide a higher pressure level than required by any of the components, in this case by the braking system. 
     However, in case the vehicle in question is usually operating under conditions with a relatively high consumption of compressed air and less frequent is used under conditions with a relatively low consumption of compressed air, the said first pressure level may be higher than the said second level. It should also be understood that the position identification means may control the operation of the power driven compressor so as to shift between not only two, but three or more different pressure levels. Thus, the foreseeable consumption of compressed air at the predetermined positions and/or positions fulfilling predetermined criteria may be further graduated. 
     The compressed air consuming devices comprises a variety of conventional apparatuses and systems. However, the more important as far as consumption of compressed air is concerned, are braking and/or air suspension systems. 
     The position identification means may be of any suitable kind being able to indicate when the vehicle is approaching or has arrived at one of a plurality of predetermined positions and/or positions where substantially higher or lower consumption of compressed air may be expected. The indication received from the position indication means may, for example, be based on map data and other information about road topology, drive pattern recognition, traffic information from external sources, sensors located on the vehicle and/or special signals generated by external sources. The information may be received by and processed in an electronic processing system, and based on predetermined criteria this processing system may determine when the air pressure level of the storage tank has to be changed. 
     In case the vehicle, such as a bus, is travelling regularly on a fixed route, said predetermined positions being selected based on experience. As an example, a plurality of plots of the consumption of pressurised air against the position along the route at different times of the day may be stored and used as a reference. Based on such experience and on the actual position along the level of air pressure of the storage tank may be decided. 
     There are locations or “predetermined positions” on a road or street where it is obvious that an extra amount of pressurised air will be needed. Examples of such locations or positions are a downhill road section, an entrance to a city area from urban areas, a specific parking location used for coupling and/or uncoupling a trailer and a specific location where the suspension of the vehicle is changed, i.e. the body of the vehicle is elevated or lowered by means of pressurised air. Such “predetermined positions” may be defined by wireless position indicators, which may be arranged at suitable place at a certain distance in advance of such predetermined position, and which may be detected by a position detector installed in the vehicle. The wireless position indicator may, for example, be a transponder transceiver and the position detector installed in the vehicle may be a transponding positioning receiver. For a bus, the predetermined positions may be the stops, where a large amount of air is needed for the buss to lower its floor and then to raise it again before continuing the trip. 
     However, in a presently preferred embodiment the position identification means comprises a global navigation system which may communicate with a receiver installed in the vehicle, and the operation of the compressor may then be controlled based on the position indication received from the navigation system combined with information about the various positions stored, such as map data, information about topology, steep road slopes, long road slopes, foreseeable traffic volume, and/or density of habitation etc. 
     The consumption of compressed air is highly dependent on the total weight of the vehicle. Therefore, less air is needed when the vehicle, such as a lorry or truck, is empty than when it is fully loaded. Therefore, the vehicle preferably includes weight-determining means, such as weight sensors or air bellow pressure sensors, for indicating whether the vehicle is empty or loaded. Such information about the load situation may be taken into consideration when controlling the operation of the compressor. This means that the pressure of the storage tank may be increased to a higher level at a certain location when the vehicle is fully loaded, but this increase may be cancelled if the vehicle is empty. 
     According to a further aspect the present invention provides a vehicle comprising a number of compressed air consuming devices, at least one storage tank for compressed air for selectively supplying compressed air to any of said devices so as to operate the same, a power driven compressor for supplying compressed air to the storage tank, pressure control means for controlling the operation of the compressor so as to maintain the air pressure in the tank substantially at a predetermined first elevated level or value, and position identification means for determining the position of the vehicle, and the vehicle according to the invention is characterised in a control device communicating with the position identification means so as to change the pressure of the compressed air in the storage tank to a predetermined second elevated level or value substantially different from said first level or value in response to receiving from the position identification means an indication to the effect that the vehicle is approaching or has arrived at one of a plurality of predetermined positions and/or positions fulfilling predetermined criteria. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The invention will now be further described with reference to the figures, wherein 
         FIG. 1  is a perspective view of a lorry including compressed air consuming devices, 
         FIG. 2  is a diagrammatic side view showing a lorry approaching a steep road slope, and 
         FIG. 3  is a diagrammatic view showing a lorry approaching an industrial area. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a perspective view showing the chassis or frame and the driver&#39;s cab of a conventional lorry or truck. The lorry comprises a power driven compressor  10  supplying compressed air to air storage tanks  11  and  12  for compressed air. The storage tanks are supplying pressurised air to a plurality of devices operated by compressed air and comprising an air suspension system, which includes a number of air bellows  13 . The compressed air consuming devices also comprise a conventional braking system not specifically illustrated in the drawings. 
     Conventionally, the operation of the compressor is controlled to maintain a pressure level in the storage tanks  11  and  12  at about 10.5 bars, or pressure range between 9.5 and 10.5 bars, as long as the velocity of the vehicle or lorry is higher than about 30 km/h and to increase such pressure to about 12 bars, or a range between 11 and 12 bars, when the velocity of the vehicle decreases to a value below 30 km/h in order to be prepared for extreme situations where there is a need of large amount of pressurised air. The maintenance of such high pressure level in the storage tanks  11  and  12  requires high energy consumption, increased wear, and an increased risk of gas/aerosol splitting off from lubricating oil in the compressor as it gets very hot, said gas/aerosol may be detrimental for sealings and gaskets. 
     The pressure level in an air system and thus in the storage tanks are monitored by pressure sensors. These sensors may be electro-mechanical sensors with a built-in hysteresis, or electronic sensors where the control system utilises a hysteresis in order to reduce the number of start/stop-cycles and/or self-oscillation of the compressor. Because of this, the term pressure level will be used meaning also a pressure range around the intended, predefined pressure level. The pressure range will in this case be substantially smaller than the pressure level itself, e.g. a pressure level of 10.5 bars will include a pressure range of approximately 9.5 to 10.5 bars. Depending on the used sensors, the pressure range will be around or below 10% of the maximum pressure level in the system. 
     In the embodiment of the present invention the operation of the compressor  10  is controlled by an electronic control device  14  which may receive control signals from internal or external sources. According to the invention the compressor  10  is operated so as to maintain the storage tanks  11  and  12  at a relative low pressure level, which is sufficient to deliver the necessary amount of compressed air to the air consuming devices  13  of the suspension and/or braking systems. However, when an actual or potential situation requiring a substantially increased consumption of compressed air is foreseen by the internal or external sources a signal may be transmitted to the control device  14 , which may then cause the compressor to increase the air pressure in the storage tanks  11  and  12  to a higher level. As an example, the lower pressure level used when the need for compressed air is estimated to be relatively low may be about 8 bars, and this level may be increased to 10 or 12 bars, when an increased consumption of compressed air is envisaged. 
       FIG. 2  illustrates a situation where a lorry or another heavy vehicle  15  is approaching a steep road slope  16 . In this case wireless position indicators, such as transponder transceivers  17  may be arranged at opposite sides of the road, and the control device  14  may comprise a wireless position detector, such a transponding position receiver. When the position detector of the control device receives a signal from the position indicators  17  indicating that the vehicle is approaching a steep road slope  16  the control device  14  may cause the compressor  10  to increase the pressure in the tanks  11  and  12  to a higher level. Alternatively or additionally the control device  14  may receive position data from satellites  18  of a global navigation system and combined with map information or topology data stored therein the control devices may decide to instruct the compressor  10  to increase the air pressure in the storage tanks. 
       FIG. 3  illustrates a similar situation where the vehicle  15  approaches an industrial area  19 . In the industrial area, there are loading docks  20  where the vehicle may load/unload goods. The industrial area may also include a trailer parking where the vehicle may pick up or park a trailer. Also in this case the control device  14  may be notified either by position indicators  17  arranged at one or both sides of the road and/or by satellites  18 . 
     It should be understood that numerous modifications and changes of the embodiments described above may be made within the scope of the appended claims. As an example the control device may receive signals from other kinds of external or internal signal sources than those described, such as video cameras, radar systems etc.