Abstract:
A closed ride control system for vehicles by which a vehicle body is suspended with respect to at least one vehicle axle and which includes the following components: pressure medium chambers which are connected via branches to a pressure medium line, a compressor, an air dryer which is arranged in a pressure medium line, a pressure medium reservoir which is connected via the compressor to the pressure medium chambers, and a non-return valve arranged in the pressure medium line between an outlet of the air dryer and the directional valve in order to connect the outlet of the air dryer to the pressure medium reservoir.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This patent application is a U.S. National Phase Patent Application of PCT International Application No. PCT/EP2009/066106, filed Dec. 1, 2009, which claims priority to German Patent Application No. 10 2009 003 472.2, filed Feb. 12, 2009, the contents of such applications being incorporated by reference herein. 
     FIELD OF THE INVENTION 
     The invention relates to a closed ride control system for vehicles by which a vehicle body is suspended with respect to at least one vehicle axle. 
     BACKGROUND OF THE INVENTION 
     A closed ride control system for vehicles of the type mentioned in the introduction is described in the European patent application EP 1 243 447 A2, which is incorporated by reference. The closed ride control device known from that document comprises two or four controllable directional valves, a pressure medium reservoir and at least two pressure medium chambers, each having a controllable directional valve. With this ride control system, pressure medium can be transferred from the pressure medium chambers to the pressure medium reservoir and vice versa. Furthermore, air from the atmosphere can be conducted into the pressure medium reservoir, the compressed air being dried in an air dryer before entering the pressure medium reservoir. In order to regenerate the air dryer, pressure medium from the pressure medium reservoir can be decompressed via a throttle and conducted to the atmosphere through the air dryer via a discharge valve, in the opposite direction in comparison to the air-drying. The regeneration of the dryer in the opposite direction is disadvantageous because it is less effective and is therefore associated with a relatively high consumption of air. Furthermore, the system contains line paths which in certain operating states remain filled with moist air, which can be removed only subsequently by additional regeneration cycles. 
     According to the closed ride control system of DE 102 31 251 C1, which is incorporated by reference, direct filling of the air springs, which may occur, for example, after a long stationary period of the vehicle, is possible, since the compressor can draw air directly from the atmosphere via an additional line leading to its inlet, which air can be conducted to the air springs directly from the outlet of the compressor. In this case, however, the direct filling of the air springs is carried out with moist air which must subsequently be dried by means of suitable regeneration cycles. 
     The regeneration cycles required for the removal of the air humidity involve additional compressor running times, since the air must first be conveyed into the system and then discharged, which must be taken into account with regard to the total service life of the compressor. These additional compressor running times entail a reduction in the availability for use of the ride control system itself, since the compressor and valves are in use longer and for thermal self-protection must periodically be left unused. Additional drying of the system air during operation of the ride control system is possible only as the air is conveyed from the air springs to the accumulator. During the conveying of air from the accumulator to the air springs, the air is diverted to the air springs upstream of the dryer. 
     An air suspension system for a vehicle, in which air always flows through the dryer as it is conveyed by a compressor, and in which both the air drying and the regeneration of the dryer take place in the same direction of flow, is known from DE 102 40 357 A1, which is incorporated by reference. The structure of this system is complicated, since a compressed-air controlled 4/3-way valve, which can be moved to three switching positions as a function of the air pressure in the system, is arranged upstream of the dryer, the first of which switching positions opens a passage of relatively large cross section through the 4/3-way valve, while the second switching position opens a throttled passage cross section and the third switching position releases a throttled discharge to the atmosphere. A regeneration of the dryer takes place in this third switching position. The compressed air for switching the 4/3-way valve is branched off upstream of the dryer and therefore contains moisture. This air cannot be dried by a system function since it is located in a part of the line without through-flow, entailing a risk of freezing-up of the 4/3-way valve, which also serves as a discharge valve. 
     SUMMARY OF THE INVENTION 
     Disclosed herein is a closed ride control system for vehicles which has a simple structure, requires little installation space, conducts air drawn from the environment through the dryer, has no paths which can be filled with moist air upstream of the dryer, and for which as small as possible a number of directional valves of simple construction is sufficient. 
     According to one aspect of the invention, a closed ride control system for vehicles by which a vehicle body is suspended with respect to at least one vehicle axle and which includes the following components:
         a) pressure medium chambers which are connected via branches to a pressure medium line,   b) a compressor,   c) an air dryer which is arranged in a pressure medium line,   d) a pressure medium reservoir which is connected via the compressor to the pressure medium chambers in such a manner that   e) pressure medium can be transferred from the pressure medium reservoir via the compressor into each pressure medium chamber, the compressor inlet then being connected via a pressure medium line through-connected by means of a directional valve to the pressure medium reservoir, and the compressor outlet then being connected via a pressure medium line through-connected by means of a directional valve to one or more of the pressure medium chambers,   f) pressure medium can be transferred from each pressure medium chamber via the compressor to the pressure medium reservoir, the compressor inlet then being connected via a pressure medium line through-connected by means of the directional valve to one or more of the pressure medium chambers, and the compressor outlet then being connected via a pressure medium line through-connected by means of the directional valve to the pressure medium reservoir, and that   g) a pressure medium line which is connectable to the atmosphere and is connectable via a directional valve, the directional valve and a pressure medium line to the compressor inlet, and is connectable via the directional valve, the pressure medium line and the directional valve to the pressure medium reservoir,   h) wherein a non-return valve is arranged in the pressure medium line between an outlet of the air dryer and the directional valve in order to connect the outlet of the air dryer to the pressure medium reservoir, in that the pressure medium line branches off from the pressure medium line at the outlet of the air dryer and upstream of the non-return valve, and in that a non-return valve and/or a throttle is/are arranged in a pressure medium line, which pressure medium line branches off from the pressure medium line at a point between the non-return valve and the directional valve and opens in the air dryer, the non-return valve blocking in the direction from the air dryer to the connection to the pressure medium line.       

     In the ride control system for vehicles by which a vehicle body is suspended with respect to at least one vehicle axle, according to aspects of the invention, a non-return valve is arranged in the pressure medium line between an outlet of the air dryer and the directional valve for connecting the outlet of the air dryer to the pressure medium reservoir; the pressure medium line to the directional valve which controls the supply and discharge of compressed air in the pressure medium line to the pressure medium chambers branches off from the pressure medium line to the pressure medium reservoir at the outlet of the air dryer and upstream of the aforementioned non-return valve; a further non-return valve and/or a throttle is/are arranged in a pressure medium line which branches off at a point between the first non-return valve and the directional valve for connecting the pressure medium line to the pressure medium reservoir and opens in the air dryer, this further non-return valve blocking in the direction from the air dryer to the point between the first non-return valve and the directional valve for connecting the pressure medium line to the pressure medium reservoir. 
     An advantage of the ride control system according to aspects of the invention can be seen in the fact that only very few controllable directional valves are required, whereby installation space and costs are saved. A further advantage is that the air drawn from the environment is always dried and that no air paths with moist air requiring additional drying or regeneration cycles are present. A reduced compressor service life combined with increased system availability is thereby made possible. The standard regeneration principle with throttle and non-return valve is retained, so that, in addition, only software changes in the control system for the normal filling of the air springs and/or of the accumulator for compressed air are required. Furthermore, additional system drying cycles can advantageously be omitted. 
     According to a development of the invention, it is provided that the throttle is arranged in the line which branches off at a point between the first non-return valve and the directional valve for connecting the pressure medium line to the pressure medium reservoir. The advantage of this arrangement is that the throttle can be arranged without difficulty in the existing components of the ride control system. 
     According to a development of the invention, the pressure medium line in which the throttle and the further non-return valve are arranged may be connected to the inlet of the air dryer or directly to a dryer bed of the air dryer. The advantage of the development of the invention with compressed air conducted directly into a dryer bed of the air dryer is that the compressed air is conducted into the dryer bed transversely to the drying flow direction of the air dryer, whereby the regeneration of the dryer is improved. 
     For this purpose the air dryer may have a dome which projects into the dryer bed and is connected to the compressed air line in which the throttle and the further non-return valve are arranged, the dome having at least one opening to the dryer bed. In this case the further non-return valve and the throttle are arranged upstream of the inlet to the dome. 
     The advantage of the last-mentioned developments of the invention is that the dryer can be combined with the dome, the non-return valves and the throttle to form a constructionally simple unit requiring little installation space. 
     According to another development of the invention, it is provided that the pressure medium line from the pressure medium reservoir to the compressor, and the pressure medium line from the pressure medium chambers to the compressor, are brought together at a point located upstream of the compressor inlet, and that non-return valves which block in the direction of the pressure medium reservoir and of the pressure medium chambers are arranged in the pressure medium lines. 
     The advantage of this development can be seen in the fact that, at a certain position of the directional valves arranged in these pressure medium lines, a flow of compressed air from the pressure medium chambers to the pressure medium reservoir is impossible, regardless of whether the air pressure in the pressure medium chambers is higher or lower than the air pressure in the pressure medium reservoir. In the rest state of the ride control system, that is, when no control is taking place, the controllable directional valves may, for example, be transferred to this rest state, so that an unintended flow of compressed air between the pressure medium chambers and the pressure medium reservoir cannot take place. In addition, as a result of such a defined state of the controllable directional valves, a measurement of the pressure in the pressure medium chambers by means of a pressure sensor is possible in a simple manner. The advantages obtained with the development are achieved while preserving all the functions of the ride control system. In particular, it continues to be possible to discharge compressed air to the atmosphere from the pressure medium reservoir via the air dryer in order to regenerate the air dryer. 
     According to a development of the invention, it is provided that a suction line is connected to the compressor inlet via a non-return valve blocking towards the atmosphere. 
     This arrangement is associated with the advantage that it makes possible rapid, direct filling of the air springs, which is desirable, for example, after a long stationary period of the vehicle. Although this rapid filling of the air springs is then possible only with moist air, this moist air can subsequently be dried by means of suitable drying cycles, so that no moist air remains in the system. 
     According to another development of the invention, the directional valves between the pressure medium reservoir and the compressor, and between the pressure medium line connectable to the atmosphere and the compressor, are switched in such a manner that aspiration of air from the atmosphere can take place only via the suction line connected via the non-return valve to the inlet of the compressor, and discharging of compressed air to the atmosphere can take place only via the from the outlet of the air dryer to the directional valve, and from there via a further directional valve through the discharge line. 
     The advantage of the development of the invention is that the air aspirated by the compressor is then always directed through the air dryer, and that the air discharged to the atmosphere via the discharge line is also directed through the air dryer, so that the air dryer is thereby regenerated. 
     An advantageous development of the invention consists in the fact that the directional valve between the pressure medium reservoir and the compressor, and the directional valve between the discharge line and the compressor, are in the form of 3/2-way valves, and the directional valves to the pressure medium chambers and in the discharge line are in the form of 2/2-way valves. 
     The advantage of this development is that the inventive ride control system requires only a minimum of directional valves of simple construction and non-return valves, reducing installation space and lowering manufacturing costs. 
     An advantageous development of the invention is that a pressure medium line with a non-return valve which blocks in the direction of the pressure medium line to the pressure medium chambers, a pressure medium line parallel thereto with a throttle between the air dryer inlet and the pressure medium line to the pressure medium chambers, and a further non-return valve, are arranged in the pressure medium line between the connections of the pressure medium lines to the non-return valve and to the throttle and to the air dryer outlet. 
     The advantage of the development is that a pressure medium flow between the pressure medium chambers and the pressure medium reservoir which bypasses the compressor and passes through the air dryer is possible, so that the major part of the moist air remaining during regeneration in the pressure medium line to the pressure medium chambers is dried. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained further below with reference to an exemplary embodiment represented in the drawing, in which: 
         FIG. 1  is a pneumatic circuit diagram of the closed ride control system according to aspects of the invention, 
         FIG. 2  is a schematic sectional view of an air dryer during a drying phase, 
         FIG. 3  is a schematic sectional view of an air dryer during a regeneration phase, and 
         FIG. 4  is a pneumatic circuit diagram of the closed ride control system according to aspects of the invention with an additional pressure medium path from the pressure medium chambers to the pressure medium reservoir. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows in a schematic representation a ride control system which is usually operated with compressed air and which includes pressure medium chambers in the form of air springs  6   a  to  6   d , a compressor  8 , an air dryer  10  and a pressure medium reservoir  12 . The pressure medium reservoir  12  is connected via a third pressure medium line  1 , which passes via a first 3/2-way valve  2   a  and a third non-return valve  31 , to a compressor inlet  14 , and also via the controllable first 3/2-way valve  2   a  and a second pressure medium line  4 , in which a first non-return valve  18  and the air dryer  10  are arranged, to a compressor outlet  16 . The first non-return valve  18  is arranged so as to open towards the pressure medium reservoir  12 . 
     A seventh pressure medium line  20 , which leads via a throttle  22  and a second non-return valve  19  to the connection between the compressor outlet  16  and the air dryer outlet  40 , branches off downstream of the first non-return valve  18 . The second non-return valve  19  is arranged so as to open in the direction of the connection between the air dryer outlet  40  and the compressor outlet  16 . 
     The air dryer outlet  40  is connected via a fourth pressure medium line  2  to a further second 3/2-way valve  4   a  which is connected via a fifth pressure medium line  3  and a fourth non-return valve  33  at a point  29  at which the third pressure medium line  1  and the fifth pressure medium line  3  are brought together and from where a connection to the compressor inlet  14  exists. 
     The third and fourth non-return valves  31  and  33  are arranged so as to open in the direction of the compressor inlet  14  and of the point  29 . 
     The second 3/2-way valve  4   a  is further connected to a first pressure medium line  34 , which is connectable via branches  38   a  to  38   d  and 2/2-way valves  26   a  to  26   d  to the air springs  6   a  to  6   d . A sixth pressure medium line  32 , in which is arranged a third 2/2-way valve  30  by means of which air can be selectively aspirated from and discharged to the atmosphere, branches off from a point  36 . 
     Furthermore, a pressure sensor  42  is connected to the first pressure medium line  34 . A suction line  5 , in which are arranged an air filter  7  and a fifth non-return valve  35  opening towards the compressor inlet  14 , also leads to the compressor inlet  14 . 
     Rapid filling of the air springs  6   a  to  6   d  and/or of the pressure medium reservoir  12  with air from the atmosphere, for example after a long stationary period of the vehicle, can be achieved in that the compressor  8  is switched on, the first and second 3/2-way valves  2   a  and  4   a  are switched to transmit in the direction of the pressure medium reservoir  12  and/or of the first pressure medium line  34 , and the 3/2-way valves  26   a  to  26   d  are moved simultaneously or successively to the open position. Because the air compressed by the compressor  8  passes first through the air dryer  10  and only afterwards into the fourth and second pressure medium lines  2  and  4 , the ride control system is filled only with dried air. 
     If compressed air is to be conveyed from one or more of the air springs  6   a  to  6   d  to the pressure medium reservoir  12 , one or more of the 2/2-way valves  26   a  to  26   d  is/are opened, the first 3/2-way valve  2   a  is moved to the position to transmit from the second pressure medium line  4  to the pressure medium reservoir  12 , and the compressor  8  is set in operation, so that the compressed air from one or more of the air springs  6   a  to  6   d  reaches the compressor  8  through the first pressure medium line  34 , the second 3/2-way valve  4   a  and the fourth non-return valve  33 , and is conveyed from there through the air dryer  10  and the first non-return valve  18  to the pressure medium reservoir  12 . 
     If, conversely, compressed air is to be conveyed from the pressure medium reservoir  12  to one or more of the air springs  6   a  to  6   d , the first 3/2-way valve  2   a  remains in the position illustrated, while the second 3/2-way valve  4   a  is moved to the position in which the fourth pressure medium line  2  is connected to the first pressure medium line  34 , so that compressed air can be conveyed by the compressor  8  from the pressure medium reservoir  12  via the air dryer  10 , the fourth pressure medium line  2 , and the second 3/2-way valve  4   a  to one or more of the air springs  6   a  to  6   d , according to the position of the 2/2-way valves  26   a  to  26   d.    
     Accordingly, both when compressed air is being conveyed from the air springs  6   a  to  6   d  to the pressure medium reservoir  12  and, inversely, from the pressure medium reservoir  12  to the air springs  6   a  to  6   d , residual moisture in the line region between the compressor inlet  14  and the third, fourth and fifth non-return valves  31 ,  33 ,  35  is conveyed through the air dryer  10  and removed from the system. 
     In order to regenerate the air dryer  10 , the first 3/2-way valve  2   a  is moved to the position transmitting from the pressure medium reservoir  12  to the second pressure medium line  4 , the second 3/2-way valve  4   a  is moved to the position transmitting from the fourth pressure medium line  2  to the first pressure medium line  34 , and the third 2/2-way valve  30  is opened to the discharge line  32 . The compressed air from the pressure medium reservoir  12  then flows via the second pressure medium line  4 , the seventh pressure medium line  20 , the throttle  22 , and the second non-return valve  19  to the connection between the compressor outlet  16  and the air dryer inlet  39 , through the air dryer  10 , the fourth pressure medium line  2 , the second 3/2-way valve  4   a , the first pressure medium line  34  and the third 2/2-way valve  30  and via the discharge line  32  into the atmosphere. 
     Through the decompression of the compressed air as a result of the throttle effect, an improved regeneration effect of the dryer granulate located in the air dryer  10  is achieved, that is, a relatively high drying effect is obtained with relatively little consumption of compressed air. 
     A line  44  for an external connection, in which a non-return valve  46  is arranged, may be provided between the air dryer outlet  40  and the first non-return valve  18 . 
     A compact construction of the air dryer  10 , in which the compressor  8 , the first and second non-return valves  18  and  19  and the throttle  22  are integrated, can be seen from  FIGS. 2 and 3 . 
     According to  FIG. 2 , the compressor  8  delivers directly to the air dryer inlet  39 , from where the compressed air reaches a dryer bed  11  and is dried. From the air dryer outlet  40 , the dried compressed air reaches the fourth pressure medium line  2  and/or the second pressure medium line  4 , the dried air flowing through the open first non-return valve  18  before entering the second pressure medium line  4 . 
     A dome  47 , represented in the form of a tube with openings  48  to the dryer bed  11 , is arranged in the dryer bed  11  and is connected via the second non-return valve  19 , the seventh pressure medium line  20  and the throttle  22  to the second pressure medium line  4 . 
     As shown in  FIG. 3 , if compressed air is directed from the pressure medium reservoir  12  via the second pressure medium line  4  to the air dryer  10 , it reaches the dome  47  through the seventh pressure medium line  20 , the throttle  22  and the second non-return valve  19 , and from there passes via opening  48  into the dryer bed  11 , from where it reaches the fourth pressure medium line  2  via the air dryer outlet  40 , and from there reaches the outside. Through the particular arrangement of the dome  47  with the openings  48 , the compressed air for regenerating the dryer bed  11  passes into the dryer bed  11  transversely to the normal flow direction, whereby the effectiveness of the regeneration process is increased. 
     It can be seen from  FIGS. 2 and 3  that the elements shown separately in  FIG. 1 , namely the compressor  8 , the air dryer  10 , the first and second non-return valves  18  and  19 , the seventh pressure medium line  20  and the throttle  22 , are combined to form a space-saving constructional unit which can be produced in a simple and low-cost manner. 
     According to the modification shown in  FIG. 4 , only the throttle  22  is arranged in the seventh pressure medium line  20 , and the line  20  opens into the dryer outlet  40 . Arranged between the air dryer inlet  39  and the fourth pressure medium line  2  are an eighth pressure medium line  49  with a non-return valve  50  which blocks in the direction of the fourth pressure medium line  2 , parallel thereto a ninth pressure medium line  51  with a throttle  52 , and in addition a seventh non-return valve  53  between the air dryer outlet  40  and the fourth pressure medium line  2  upstream of the connections of the eight and ninth pressure medium lines  49  and  51 . It is thereby made possible to establish a direct connection from the pressure medium chambers  6   a  to  6   d  to the pressure medium reservoir  10 , the flow bypassing the compressor  8  but passing through the air dryer  10 , in order to bring about a pressure equalization between the pressure medium chambers  6   a  to  6   d  and the pressure medium reservoir  12 , and a drying of the compressed air when the pressure in the pressure medium reservoir  12  is lower than in the pressure medium chambers  6   a  to  6   d.