Abstract:
An air suspension system for a load bearing vehicle which includes a pair of air springs fluidly connected to a pair of auxiliary air reservoirs and to a main air reservoir. The system includes control valves which permit the air in the air springs to be exhausted therefrom to lower the vehicle frame without exhausting the air from the auxiliary air reservoirs.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to an air suspension system for a vehicle and more particularly to an air suspension system for a vehicle which is designed to permit one end of the vehicle to be lowered or kneeled. Even more particularly, the air suspension system of this invention permits the exhaust of air from the air springs of the suspension system, while preventing the exhaust of air from the auxiliary air reservoirs of the suspension system. 
   2. Description of the Related Art 
   Link Manufacturing, Ltd. (“Link”) of Sioux Center, Iowa, markets an air suspension system under the trademark ULTRARIDE®. In the ULTRARIDE® system of Link Manufacturing, a pair of air springs are utilized to support the rear axle of the vehicle frame. In Link&#39;s prior art suspension system, the air may be exhausted from the air springs so that the rearward end of the vehicle frame may be lowered for loading purposes such as is desirable with shuttle buses, ambulances, etc. When the air springs are reenergized, the air compressor (the air source for the suspension system) may be unduly taxed which may potentially decrease its life. Further, in Link&#39;s prior art system, it takes some time to bring the vehicle to ride-height again which reduces the “drive away time,” which creates problems in the EMS industry where “drive away time” is critical and the vehicle needs to return to ride-height quickly. 
   SUMMARY OF THE INVENTION 
   An air suspension system is described for a load-bearing vehicle including first and second longitudinally extending frame members with an axle positioned therebelow. The vehicle is provided with a source of air under pressure such as a compressor which supplies air to a main air reservoir or tank which in turn supplies air to a pair of air springs positioned between the frame members and the axle with the amount of air provided thereto being controlled by either a first height control valve or first and second height control valves. In one embodiment of this invention ( FIG. 5 ), first and second auxiliary air reservoirs are mounted on the frame members with each of the auxiliary air reservoirs having inlet and outlet ends. First and second air dump valves are also provided with each of the air dump valves having a first port, a second port and an exhaust port. The first ports of the first and second air dump valves are in fluid communication with the outlet ends of the first and second auxiliary air reservoirs, respectively. The second ports of the first and second air dump valves are in fluid communication with the air inlet/outlet ports of the first and second air springs, respectively. Each of the first and second air dump valves are movable between first and second positions. The first and second air dump valves, when in their first position, permit fluid communication between the respective auxiliary air reservoirs and the inlet/outlet ends of the respective air springs by way of the first and second ports thereof. The exhaust port of each of the first and second air dump valves is closed when the air dump valves are in their first position. The air dump valves, when in their second position, permit the air in the respective air springs to be exhausted therefrom through the exhaust ports of the first and second air dump valves. The first ports of the first and second air dump valves are closed when the first and second air dump valves are in their second position. 
   When the air dump valves are moved to their second position so that air may be exhausted from the air springs to lower the vehicle frame, the air in the auxiliary air reservoirs is not exhausted to the atmosphere. When the air dump valves are in their first position, the auxiliary air reservoirs act as accumulators in conjunction with the air springs thereby lowering the spring rate of the system and improving the ride thereof. 
   The embodiment of  FIG. 6  is substantially identical to the embodiment of  FIG. 5  except that only a single height control valve is utilized. 
   In a further embodiment of the invention ( FIGS. 3 and 4 ), first and second auxiliary air reservoirs are mounted on the frame members with each of the auxiliary air reservoirs having an inlet/outlet end. First and second control valves, having first and second ports, are also provided with the second ports thereof being connected to the inlet/outlet end of the auxiliary air reservoirs, respectively. The first ports of the control valves are in communication with a pair of air springs. The first and second control valves are movable between open and closed positions. In the embodiment of  FIG. 3 , first and second air dump valves, having a first port, a second port and an exhaust port are also provided. The first port of each of the air dump valves is connected to a height control valve with the second port of each of the air valves being operatively connected to the second port of the associated control valve and the inlet/outlet end of the air spring. In the embodiment of  FIG. 3 , each of the first and second air dump valves is movable between first and second positions. When the dump valves are in their first position, the control valves are in their open position. When the dump valves are in their second position, the control valves are in their closed position. The first and second control valves, when in their open position, permit fluid communication between the respective auxiliary air reservoirs and the inlet/outlet ends of the respective air springs by way of the first and second ports thereof. The exhaust ports of the first and second air dump valves are closed when the air dump valves are in their first position. The air dump valves, when in their second position, permit the air in the respective air springs to be exhausted therefrom through the exhaust ports of the first and second air dump valves. The first ports of the first and second air dump valves are closed and the control valves are in their closed position when the first and second air dump valves are in their second position. 
   In this embodiment, when the air dump valves are moved to their second position so that air may be exhausted from the air springs to lower the vehicle frame, the air in the auxiliary air reservoirs is not exhausted to the atmosphere since the control valves are in their closed position. 
   The embodiment of  FIG. 4  is essentially the same as the embodiment of  FIG. 3  except that a single air dump valve is utilized rather than a pair of air dump valves. When the dump valves are in their first position, in all of the embodiments of  FIGS. 3 ,  4 ,  5  and  6 , the auxiliary air reservoirs act as accumulators in conjunction with the air springs thereby lowering the spring rate of the system and improving the ride thereof. 
   It is therefore a principal object of the invention to provide an improved air suspension system for a vehicle. 
   A further object of the invention is to provide an air suspension system for a vehicle wherein the air in the air springs may be exhausted therefrom to lower the frame into a “kneeling” position without exhausting the air from auxiliary air tanks operatively connected to the air springs. 
   A further object of the invention is to provide an enhancement kit for Link Manufacturing&#39;s ULTRARIDE® air suspension systems. 
   These and other objects will be apparent to those skilled in the art. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partial perspective view of the vehicle frame having the air suspension system of this invention mounted thereon; 
       FIG. 2  is a side view of the suspension system of  FIG. 1 ; 
       FIG. 3  is schematic of one embodiment of the system of this invention employing dual height control valves; 
       FIG. 4  is a schematic view of a second embodiment which is similar to that of  FIG. 3  except that only a single height control valve is utilized; 
       FIG. 5  is a schematic of the suspension system of a third embodiment of this invention which utilizes a pair of height control valves and a pair of control valves; and 
       FIG. 6  is a schematic view of a fourth embodiment which is similar to that of  FIG. 5  except that the system therein utilizes only a single height control valve. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The numeral  10  refers generally to a vehicle such as a truck, ambulance, shuttle bus, bus, etc., with the vehicle  10  including a pair of longitudinally extending frame members  12  and  14 , as illustrated in  FIG. 1 . Although the drawings herein illustrate the suspension system as being utilized on the rear of the vehicle, the suspension system could also be used at the forward end of the vehicle, if so desired. For purposes of illustration,  FIG. 1  depicts the embodiment of  FIG. 4  although the air dump valve is not shown. Although a particular air suspension system is shown in  FIGS. 1 and 2 , the system of this invention may be used on all suspension designs, not just the Link ULTRARIDE® suspension system. 
   In all the embodiments of  FIGS. 3 ,  4  and  5 ,  6 , mounting brackets  16  and  18  are secured to the frame members  12  and  14 , respectively, forward of the rearward end thereof. Beams  20  and  22  are pivotally connected at their forward ends to the brackets  16  and  18 , respectively, in conventional fashion. A transversely extending axle  24  is secured to the beams  20  and  22  forwardly of their rearward ends thereof, as illustrated in  FIG. 1 . The opposite ends of the axle  24  are adapted to have wheels mounted thereon in conventional fashion. The rearward ends of the beams  20  and  22  have supports  26  and  28  provided thereon, respectively, which have air springs  30  and  32  mounted thereon. The upper ends of the air springs  30  and  32  are secured to mounting brackets  33  and  35  which are secured to frame members  12  and  14  in conventional fashion. Air springs  30  and  32  have inlet/outlet ports  34  and  36  provided thereon, respectively, as will be described in more detail hereinafter. 
   In the embodiment of  FIG. 4 , a height control valve  38  is interconnected between the bracket  16  and the beam  20  and has its inlet port  40  in communication with the main air reservoir  42  which is filled with air under pressure by an air compressor. In the situations where a pair of dual height control systems are utilized ( FIG. 3 ), a height control valve  38 ′ is also utilized with the intake port  40 ′ thereof being connected to the air supply reservoir  42 . In the single height control embodiment of  FIG. 4 , a dump valve  43 , which is movable between first and second positions, has its inlet port  44  in fluid communication with the outlet port  46  of height control valve  38 . In the dual height control system of  FIG. 3 , a second dump valve  43 ′ is utilized with the inlet port  44 ′ thereof being in communication with the outlet port  46 ′ of height control valve  38 ′. Each of the dump valves  43  and  43 ′ are movable between first and second positions. 
   In the single height control system, as illustrated in  FIG. 4 , the outlet port  48  of dump valve  43  is in communication with the air springs  30  and  32  and control valves  50  and  52 , with the control valves  50  and  52  being fluidly connected to auxiliary reservoirs  54  and  56 , respectively. The control valves  50  and  52  are automatically movable between open and closed positions. 
   In the dual height control system of  FIG. 3 , the outlet port  48 ′ of dump valve  43 ′ is fluidly connected to the air spring  32  and the control valve  52 , with the control valve  52  being connected to the auxiliary reservoir  56 . When the dump valves  43  and  43 ′ are in their first positions, the control valves  50  and  52  are in their open position. When the dump valves  43  and  43 ′ are in their second positions, the control valves  50  and  52  are in their closed position. When the dump valves  43  and  43 ′ are in their first position, air flows from the height control valve or valves, through the dump valves  43  and  43 ′, and into the air springs  30  and  32 . When the dump valves  43  and  43 ′ are in their second position, air from the air springs  30  and  32  is exhausted to the atmosphere by way of the exhaust ports thereof. 
   In the single height control system of  FIG. 4 , when it is desired to dump the air from air springs  30  and  32  so that the frame of the vehicle may be lowered, the dump valve  43  is moved to its second position so that the air from the air springs  30  and  32  is dumped from the system through the exhaust port of the dump valve  43 . Control valves  50  and  52  are automatically closed which prevents the air in the auxiliary air reservoir from being dumped to the atmosphere. When it is desired to again raise the frame, the dump valve is moved to its first position and the air compressor supplying air to the air supply reservoir  42  is actuated to supply air to the air springs  30  and  32  if sufficient pressure is not present in the air supply reservoir. The dual height control system illustrated in  FIG. 3  functions in the same manner as just described for the single height control system of  FIG. 4  with the exception being that two height control valves and two dump valves are utilized. 
     FIGS. 5 and 6  illustrate further embodiments which are also designed to improve the recovery time after air has been dumped from the air springs.  FIGS. 1 ,  2  and  6  illustrate a single height control system of this invention including a height control valve  38  having an inlet port  40  connected to air supply reservoir  42 . The outlet port  48  of height control valve  38  is fluidly connected to auxiliary reservoirs  54  and  56 . Line  70  extends from height control valve  38  to auxiliary reservoir  54  to fluidly connect the same. Line  72  is tapped into line  70  and supplies air to the auxiliary reservoir  56 . Large diameter air lines  76  and  78  fluidly connect auxiliary reservoirs  54  and  56  to three-way dump valves  80  and  82 , respectively. A large diameter line  84  fluidly connects the outlet port  86  of the dump valve  80  to the air spring  30 . A large diameter line  88  connects the outlet port  90  of dump valve  82  to air spring  32 . 
   Each of the dump valves  80  and  82  are movable between two positions. When the dump valves are in the first position, as illustrated in  FIG. 6 , the auxiliary reservoir  54  and the main air supply reservoir  42  supply air under pressure to the air spring  30  through the large diameter air lines  76  and  84  positioned on opposite sides of the dump valve  80 . When the dump valve  80  is in its first position, as illustrated in  FIG. 6 , the exhaust port  92  thereof is closed. Similarly, when the dump valve  82  is in the first position illustrated in  FIG. 6 , the air supply reservoir  42  and auxiliary reservoir  56  supply air under pressure to the air spring  32  through the large diameter air line  78 , valve  82  and large diameter air line  88 . In the position illustrated in  FIG. 6 , the auxiliary reservoirs  54  and  56  act as accumulators in conjunction with the air springs  54  and  56 , thereby lowering the spring rate of the system and improving the ride. It is recommended that the auxiliary reservoirs  54  and  56  be placed in close proximity to the air springs  30  and  32 , respectively, in order to achieve the most benefit of the system. It is also recommended that the air lines  76 ,  84 ,  78  and  88  be large diameter air lines so that they do not restrict the flow of air between the air springs and the reservoirs. When the dump valve  82  is in its first position illustrated in  FIG. 6 , the exhaust port  94  of dump valve  82  is in its closed position. 
   When it is desired to dump the air from air springs  30  and  32  so that the frame may be lowered with respect to the ground, the dump valves  80  and  82  are operated so as to move the same from their first position to their second position. When the dump valves  80  and  82 , respectively, are in their second position, the air flows from the air springs  30  and  32  through the valves  80  and  82  and out the exhaust ports  92  and  94  thereof, respectively. When the dump valves  80  and  82  are in their second position, the inlet ports of the dump valves  80  and  82  are in their closed position so that the air in the auxiliary reservoirs is not dumped therefrom. When it is desired to again raise the frame, the dump valves  80  and  82  are moved to their first position so that air again may be delivered to the air springs  30  and  32 . The fact that the auxiliary reservoirs  54  and  56  are not dumped when the dump valves  80  and  82  are moved to their second or dumping position, enables air to be quickly supplied to the air springs  30  and  32 . As stated, upon reenergizing the air springs, air from the main air reservoir  42  flows through the height control valve  38  and into the air springs  30  and  32  until the vehicle achieves the correct ride height, as controlled by the height control valve  38 . 
   The dual height control system of the embodiment of  FIG. 5  functions essentially the same as the single height control system of  FIG. 6  except that a second height control valve  38 ′ is plumbed or connected to the auxiliary reservoir  56 . The dump valves  80 ,  82  and the air springs  30 ,  32  in the embodiment of  FIG. 5  are identical to that described with respect to the embodiment of  FIG. 6 . 
   The control valves  50  and  52  in either embodiment may be either an air piloted valve, solenoid valve, pressure protection valve, or any other type of control device which enables the air in the auxiliary reservoirs  54 ,  56  to be isolated from the air springs  30 ,  32 . This operation improves compressor life, and also provides an initial boost to the air springs when they are returning to ride height. The initial air flow to the air springs is especially important for the EMS industry where “drive away time” is critical and the vehicle needs to return to ride height quickly. In all of the embodiments, the reservoirs  54  and  56  act as accumulators in conjunction with the air springs  30  and  32 , thereby lowering the spring rate of the system and improving the ride. 
   Thus it can be seen that the invention accomplishes at least all of its stated objectives.