Suspension and leveling system for a vehicle
BACKGROUND OF THE INVENTION 
     The present invention relates to a suspension and leveling system for a vehicle. 
     Many vehicles include suspension systems which are controlled by shock absorbers and by leaf springs. In many heavy systems such as found in motor homes, the ride provided by shock absorbers and leaf springs is rough, and not satisfactorily smooth. 
     It is also desirable with motor homes to be able to level the motor home after it has been parked in a position for use overnight. 
     Therefore, a primary object of the present invention is the provision of an improved suspension system for a vehicle. 
     A further object of the present invention is the provision of an improved suspension system which can be adapted to the present suspension systems found in many vehicles. 
     A further object of the present invention is the provision of an improved suspension system which provides a smooth pneumatic suspension system for supporting the vehicle while it is being driven. 
     A further object of the present invention is the proof a suspension system which can be adapted to present vehicles by altering or removing the leaf springs currently found on present vehicles. 
     A further object of the present invention is the provision of a suspension system which permits the selective leveling of the device as desired. 
     A further object of the present invention is the provision of a suspension system which includes automatic height control valves for automatically leveling the system if desired. 
     A further object of the present invention is the provision of a pneumatic air bag suspension system which includes also an accumulator tank for accumulating condensation which occurs within the pneumatic system during increases and decreases of atmospheric pressure. 
     A further object of the present invention is the provision of a pneumatic air bag suspension system which also includes an accumulator tank for increasing the effective volume of air which is compressed within the air bag so as to create a softer suspension. 
     A further object of the present invention is the provision of a suspension system which includes a radius rod for providing horizontal stability to the axle with respect to the vehicle. 
     A still further object of the present invention is the provision of an air suspension system which is economical to manufacture, efficient in operation and simple to install. 
     SUMMARY OF THE INVENTION 
     The present invention can be adapted to a vehicle having a conventional leaf spring suspension system. The leaf spring is cut in half, and the rear half of the leaf spring is removed. An air bag is mounted between the cut off end of the leaf spring and the vehicle frame. The air bag is supplied by a pneumatic system which includes an accumulator tank attached to the vehicle frame and in fluid communication with the air bag. 
     Means are provided in the pneumatic system for varying the air pressure of the air within the air bag and the accumulator tank. This permits the adjustment of the height of the vehicle frame above the axle. 
     The accumulator tank increases the softness of the ride. The accumulator tank is connected to the air bag so that as air is compressed in the bag, it also is compressed in the accumulator tank, resulting in a softer ride. The accumulator tank also includes a drain valve, and any condensation which results from variance in the air pressure, will accumulate in the accumulator tank and can be drained by opening the drain valve. 
     The accumulator tank enhances the softness of the ride by enlarging the effective volume of the air bag. This is desirable, because the diameter of the air bag is limited, thereby limiting the ability to provide the proper air volume to create the desired softness of ride. 
     A stability rod is attached at one end to the vehicle frame and extends transversely of the vehicle frame to the point where it is connected to the axle. This stabilizer rod permits the axle to move vertically with respect to the vehicle frame, but holds the vehicle frame in centered relation over the axle so that it does not move laterally with respect to the axle. 
     A control system is provided for controlling the pressure within the air bag. The control system includes electrical switches which can be mounted within the vehicle cab. The switches are connected to various valves in the pneumatic system which supplies the air bag. The control system can be placed in an automatic mode which employs height control valves for maintaining a constant distance between the vehicle frame and the axle in response to variations in load distributions within the vehicle. The control system can also be placed in a manual mode for leveling the vehicle when it is parked on an uneven supporting surface. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS 
     FIG. 1 is a side elevational view of a motor home. 
     FIG. 2 is a sectional view through a motor home showing the axle and suspension system of the present invention. 
     FIG. 3 is a sectional view taken along line 3--3 of FIG. 2. 
     FIG. 4 is a partial top plan view taken along line 4--4 of FIG. 3, but showing only one-half of the vehicle frame. 
     FIG. 5 is a perspective view of a modified form of the present invention. 
     FIG. 6 is a sectional view taken along line 6--6 of FIG. 3. 
     FIG. 7 is an enlarged detail elevational view of the height control linkage and height control valve used in the present invention. 
     FIG. 8 is a schematic diagram showing the pneumatic and electrical circuitry for the present invention. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Referring to the drawings, the numeral 10 generally designates a motor vehicle as shown in FIG. 1. Vehicle 10 includes a vehicle cab 12, a vehicle frame 14 having two side members 16 and 18, and a number of cross members 20. Vehicle 12 also includes an axle 22 which extends transversely of the vehicle frame 14 and which is positioned below vehicle frame 14. 
     A leaf spring 24 includes a first end 26 which is pivotally connected to vehicle side frame 16 for pivotal movement about an axis 28. Leaf spring 24 is shown to be severed at its approximate middle so as to create a second free end 30. The remaining portion of the leaf spring found originally on the vehicle is discarded, leaving only the portion which terminates at end 30. 
     An air bag 32 includes an upper bag frame 34 which is attached to vehicle frame member 16 by means of bolts 35. 
     Air bag 32 also includes a lower bag frame 36 which is adapted to be connected to a Z-shaped mounting plate 38 having a lower horizontal plate member 40, a vertical plate member 42, and an upper horizontal plate member 44. Located between upper bag frame 34 and lower bag frame 36 is a flexible rubber bag 46 which defines an air bag compartment 48 (FIG. 6). In communication with air bag compartment 48 is an inlet opening 50 which is connected to an air hose or conduit 52. 
     Prior to the modification of the suspension system of the vehicle, the axle 22 is attached to the leaf spring 24 by means of a pair of U-shaped clamps 54 which extend through leaf spring 24 and which also extend through a pair of axle brackets 56, 58 which surround axle 22. The U-shaped bolts 54 are tightly secured to leaf spring 44 and axle brackets 56, 58 by means of nuts 60 which are threaded on the lower ends of U-shaped bolts 54. 
     In modifying a conventional suspension system to provide the present invention, the U-shaped bolts 54 are loosened, and the upper horizontal plate 44 is inserted between the leaf spring 24 and the axle brackets 56 as shown in FIG. 3. Then the nuts 60 are tightened, thereby securing the lower bracket 36, and the second end 30 of spring 24, rigidly to the axle 22 as shown in FIG. 3. This causes the weight of the vehicle frame to be borne jointly by the spring 24 and the air bag 32. The axle is also partially supported by conventional shock absorbers 62. Approximately 80% of the load from frame 14 is borne by air bag 32. 
     Air hose 52 leads from air bag 32 to an accumulator tank 64 which is mounted to vehicle frame 16 and which includes a condensation drain valve 66 therein. In FIG. 3, accumulator tank 64 is schematically shown in reduced scale. Preferably the accumulator tank 64 should have a volume equal to or greater than bag compartment 48. Accumulator tank 64 provides two functions. First, it adds to the effective volume of air compressed within air bag 32, thereby enhancing the smoothness of ride provided by air bag 52 while the vehicle is moving over a supporting surface. Also, accumulator tank 64 acts as an accumulation point for condensation which forms in the pneumatic system, and drain valve 66 permits the draining of this condensation from the system. This is important because conventional air bags such as air bag 32 do not normally provide for removal of condensation. 
     An air control system is shown schematically in FIG. 8 and is designated generally by the numeral 68. Control system 68 includes an air compressor 70 which is electrically connected to the ignition 72 for receiving power from the vehicle battery 74. A pressure gauge 76 is connected to air compressor 70 and is mounted within the cab 12 of vehicle 10 for monitoring by the operator. 
     Air compressor 70 is fluidly connected to a pressure tank 78 which in turn is connected to a pneumatic loop which includes two height control valves 80, a pair of automatic valves 82, a pair of down valves 84, and a pair of up valves 86. This loop is connected pneumatically to the accumulator tanks 64 which in turn are connected by hoses 52 to air bags 32. Each of the automatic control valves 82 is connected to an automatic control valve solenoid 88. Each of the down valves 84 are connected to a down valve solenoid 90, and each of the up control valves 86 is connected to an up control valve solenoid 92. Automatic control valve solenoids 88 are connected to a first terminal 94 of a master control switch 96. Master control switch 96 can move between the first terminal 94 and a second terminal 98. When switch 96 is in contact with terminal 94, solenoids 88 are actuated to move the automatic control valves 82 to their open positions. This permits fluid pressure to pass from pressure tank 78 through height control valves 80 to accumulator tank 64 and air bags 32. The height control valves 80 are movable between open and closed positions, and are controlled by linkages which extend from the height control valves to the axles of the vehicle as shown in FIGS. 2 and 3. The height control valves 88 are mounted to the vehicle cross frame member 20. Extending from the height control valves 88 are a first mechanical link 100 and a second link 102 which are pivotally connected to one another. The lower end of link 102 is attached to axle 22. Thus, as the distance between axle 22 and vehicle frame member 20 increases or decreases, the linkage 100, 102 causes the valve 88 to be manually moved to different positions. The valve 88 is adapted to be moved to its open position whenever the distance D between vehicle frame 20 and axle 22 is less than a predetermined distance. In this case, the valve 88 is opened by means of linkage 100, 102, and air pressure is introduced from the pressure tank 78 to the air bags 32, thereby causing the air bags 32 to function as a pneumatic cylinder for raising the vehicle frame until the desired distance D is achieved. When the pre-selected desired distance D is achieved, the linkage 100, 102 senses this difference, and causes the height control valve 88 to close, thereby preventing any further pressure from being introduced to air bag 32. As can be seen in FIGS. 2 and 3, the two height control valves 80 operate independently of one another, thereby permitting either the left or right hand side of the vehicle to be raised or lowered as desired. The pre-setting of height control valves 88 can cause the vehicle to maintain a level position even though the load within the vehicle may be unevenly distributed. 
     An example of a height control valve which is preferred for the present invention is a valve manufactured by Nelson Metal Products Company, 2950 Prairie Street, Granville, Mich. 49418, under the registered trademark &#34;Hadley&#34; and designated as the 450 Series. The valve is capable of providing a two to six second time delay so that the valve will not respond to normal jostling or bumping during riding, but will only respond to a permanent change in the distance D which lasts longer than two to six seconds. 
     Referring again to the schematic of FIG. 8, the device may be changed from an automatic mode to a manual mode by moving master control switch 96 from terminal 94 to terminal 98. This causes the automatic valves 82 to move to their closed position, thereby preventing the height control valves 80 from having any effect upon the air pressure within air bags 32. 
     In the manual mode, the battery 74 is connected through master control switch 96 and terminal 98 to a pair of up-down switches 104. Up-down switches 104 are manually movable to an up position in connection with terminals 106. Switches 104 are also movable to a down position in connection with terminal 108. When switches 104 are in their up position they cause solenoids 92 to move the up valves 86 to their open position. This permits fluid pressure from pressure tank 78 to move through up valves 86 to the air bags 32. Thus the operator can manually move valve 104 to the up position and cause a lifting of the particular bag desired so as to achieve leveling of the device. The two switches 104 permit independent operation of the two air bags 32. Up valves 86 are in their closed position except when switches 104 are in their up position in connection with terminals 106. 
     If it is desired to lower one side of the vehicle, the switches 104 are manually moved to the down position in connection with terminals 108. This causes solenoid 90 to move down control valve 84 to an open position wherein air can escape from air bag 32 through valve 84 outwardly to the atmosphere by means of an escape valve 110. Switches 104 are preferably toggle switches which are normally centered in a position out of contact with both terminals 108 and 106. Switches 104 can be manually moved either into contact with terminals 106 or terminals 108, as desired to raise or lower one particular side of the vehicle. 
     The automatic mode can again be placed in operation by moving master control switch 96 from the manual position in contact with terminal 98 to the automatic position in contact with terminal 94. This again opens the automatic control valves 82 and makes the height control valves 80 effective as previously described. At the same time, the down control valve 84 and the up control valves 92 automatically move to their closed positions. 
     Referring to FIG. 5, a modified form of spring can be used to replace the leaf spring 24. The modified form of spring includes a hinge 112 which can be connected to vehicle frame 16 in a fashion similar to that shown at 28 for leaf spring 24. Leaf spring 24 includes an upper arcuate portion 114, a vertical portion 116, and a lower horizontal portion 118. With the use of the member (designated generally by the numeral 120) in FIG. 5, it is possible to eliminate the Z-shaped member 38 shown in FIG. 3, and to directly connect the air bag 32 to the lower horizontal portion 118 of member 120 as shown in FIG. 5. Then U-bolts 54 are used to clamp the end 122 of arcuate portion 114 to the axle in a fashion similar to that shown for the leaf spring 24 of FIG. 3. The advantage of the use of member 120 is that a single continuous member extends from axis 28 to the lower end of air bag 32 whereas the configuration shown in FIG. 3 requires the use of an intermediate Z-shaped mounting plate 38. 
     The present invention provides many advantages. The steel leaf spring which normally provides the sole support for the axle, is replaced by the rubber air bag, thereby supporting the axle pneumatically and providing a smoother ride on the column of air provided by the air bag. 
     The device permits the compensation for load variations by permitting more air to be pumped into the bag when the load is increased, and by permitting the removal of air from the bag when the load is decreased. 
     The height control valves provide a constant maintenance of the distance from the frame to the axle, regardless of changes in the load distribution within the vehicle. The height control valve on each side of the frame keeps the distance constant. This is done by the linkage 100, 102 which is hooked to the axle and the height control valve 88 which is connected to the frame. As the frame moves up and down, it either calls for more air and fills the air bag to raise the frame, or it calls for exhausting the air to let the frame down. 
     The air bag provides the large majority of the bearing of the load on the axle. It is positioned behind the axle so that it carries approximately 80% of the load. 
     In the modification shown in FIG. 3, the front half of the original leaf spring is kept. Some flexibility is still maintained in the front half of this spring. It has been found that the positioning of the air bag as shown in FIG. 3 slightly behind of the axle provides the maximum smoothness of ride. Furthermore, the use of a flexible member such as leaf spring 24 or such as member 120 also provides a smoother ride than if a rigid member is used. 
     The softness of ride is further enhanced by using the accumulator chamber 64. When the air is compressed within the air bag, it is also compressed in the accumulator chamber which results in a softer ride. The air from the compressor and the reserve air tank must first pass through the accumulator tank, and this permits any condensation to be trapped in the accumulator tank so as to minimize the accumulation of water in the air bag. A drain valve is provided at the bottom of the accumulator tank to permit condensation to be drained away. 
     A more desirable ride can be obtained by using the air bag in combination with the accumulator tank. This ride is more desirable than is obtained by increasing the diameter of the bag without using the accumulator tank. With the larger diameter bag, the air pressure within the bag is reduced, but doing this also reduces the spring rate and results in a rougher ride. By using the accumulator tank, it is possible to keep the air pressure within the air bag slightly higher, while at the same time providing a greater volume of air which can be compressed within the accumulator tank. This produces the desired softness of ride. 
     For lateral stability of the vehicle frame with respect to the axle, a radius rod 124 has one end pivotally connected to the vehicle frame 14 about horizontal axis 126 and has the opposite end connected to axle 22 for pivotal movement about horizontal axis 128. Stabilizer rod 124 is an elongated bar, and the opposite ends can be connected to the axle and frame respectively by solid rubber bushings on each end of the rod. The radius rod keeps the body of the vehicle directly centered over the axle. It is possible to split the radius bar longitudinally so that it can also be used as a torsion bar, thereby allowing for twist along its longitudinal axis. 
     The height of the vehicle remains constant. This is done by the height control valves which are mounted to the frame and which are connected to the axle by means of linkages 100, 102. As the load changes, it calls for either an increase of air in the air bags, or an exhasting of air from the air bags to maintain a preset height. The height control valve has approximately a five second delay inherent therein so as to prevent unnecessary reaction to holes and bumps in the road. It only responds to changes in the load on the vehicle which lasts longer than five seconds. 
     The system is supplied with a 12 volt air compressor that runs on demand by a pressure switch on the air tank. 
     The present device also provides a manual option which pemits the leveling of the device when it is parked. In conventional devices, this is done by the use of hydraulic jacks which are located at the four corners of the vehicle. 
     The present invention converts the air bags into air cylinders which can raise and lower the opposite sides of the vehicle. In order to do this, the master switch is placed in the manual mode and the manual switches 104 are actuated either to raise or lower the sides of the vehicle. 
     One variation of the present invention comprises placing the height control valves on a slide which permits them to move vertically with respect to the frame. An electrical motor, worm gear, or other conventional electrical moving device can be used to raise and lower the height control valves with respect to the frame. This will result in changing of the heights of the air bags when the system is in its automatic mode. The same result can be obtained by using extensible links which can be lengthened or shortened to cause the height control valves to change the pressure within air bags 32. 
     Thus, it can be seen that the device accomplishes at least all of its stated objectives.