Abstract:
A suspension system for the steering axle of a vehicle chassis includes a right side air spring and a left side air spring. In the preferred embodiment leading rigid arms link each end of the steering axle to a pivoting mount on the chassis and transmits brake reaction torque as a lifting force to the chassis. Spring half leaf trailing links connect each end of the steering axle to the chassis, rigid leading arms provide anti-roll capacity as well as help in locating and stabilizing axle position.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to vehicle front end suspension systems and, more particularly, to an air spring based suspension system directed to improving vehicle stability by reducing front end dive during braking and increasing resistance to vehicle roll during cornering. 
     2. Background 
     Truck suspension systems are designed to meet each of several not wholly compatible goals which include: absorbing road shock and providing a comfortable ride; stabilizing the vehicle, especially during cornering and braking, to help the driver keep control of the vehicle; and maintaining proper axle spacing and alignment, which also helps to keep the vehicle under control and extend tire life. These goals must met while supporting the vehicle&#39;s weight over a wide range of vehicle load conditions. 
     There are four basic categories of suspension systems used on trucks: leaf spring systems; equalizing beam systems; torsion bar systems; and air spring systems. The categories are not mutually exclusive and elements of more than one system may be combined to build a hybrid suspension system, at some cost both in terms of money and complexity. 
     Air spring systems have recently gained in popularity and have been applied to a variety of truck axles, including of particular interest here, the steering axle. Air spring suspensions give excellent load and vibration isolation to the cab by eliminating the interleaf friction found in traditional multiple leaf spring designs. The deflection rate of air springs can be adjusted automatically to compensate for vehicle load changes. As a result, vehicle height does not vary with load or positioning of the load, thereby enhancing driver control. In addition, an air spring usually has a lower deflection rate than a leaf spring exerting the same force giving the system greater capacity for absorbing shocks for a given displacement between the axle and the frame. 
     Air springs are also employed to maintain a constant vehicle height despite changes in vehicle loads. As such it may sound odd to refer to a deflection rate for such springs since the deflection rate for a compression spring equates spring deflection with force generated. Air springs, unlike conventional springs, can be and are used to generate a varying amount of force while maintaining a fixed height displacement. This is effected by changing air pressure in the air spring in response to changes in vehicle height, either dumping or adding air to the air spring by valves. Conventional springs must of course deflect to generate a balancing counter force. In effect, as air pressure is changed in an air spring in order to maintain a constant height, the deflection rate of the spring is changing. Thus, air springs may be termed controllable rate springs or controllable deflection springs. 
     In an air spring based system, air bellows are positioned with respect to an axle and a vehicle frame to support the frame from the axle. The air spring can be used to supplement a leaf spring arrangement by being placed between the leaf spring and the vehicle frame. Commonly though, air spring systems replace the leaf spring. In a typical application of air springs to a steering axle, an air spring is placed adjacent each wheel over the axle and directly below the side rails of the vehicle frame. 
     Pure air spring based systems are not without problems. Air springs, for all of their advantages in providing a comfortable ride and adaptability to changing load conditions, have required substantially more complex and costly suspension designs than have leaf springs. A leaf spring provides two frame mounting points fore and aft of the steering axle to aid in axle stabilization and location, whereas an air spring provides nothing in the way of axle stabilization and location. An air spring suspended steering axle has typically been stabilized using trailing connecting rods or arms between the frame rails and the steering axle. A lateral track bar has provided lateral stabilization for the axle. Trailing arm systems achieve substantial front end anti-roll stiffness by positioning rigid arms between the frame and the axle, with each arm being pivotally attached to the frame and rigidly attached to the axle. The trailing arm design used with air springs at the vehicle front end is not without disadvantages. During vehicle braking, the front ends of vehicles tend to dive. In traditional leaf spring suspension designs, where the leaf spring is mounted to the frame at two points, ahead of the solid axle and following the axle, the torque reaction force generated by the brakes on the axle in turn generates a reactive upward force on the frame through the leaf springs aft mounting point and a downward reactive force through the forward mounting point. No net downward force is transmitted from braking. In trailing arm/air spring suspension designs this balance is lost. Trailing arm designs transmit the brake reaction torque to the frame only through the forward trailing arm mount as a downward force and thereby increase dive. Most trailing arm designs are also poor at maintaining axle position laterally, necessitating the use of a lateral track bar to hold axle position. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide an air spring suspension system with improved vehicle stability characterized by increased resistance to front end dive on braking and improved resistance to roll. 
     It is another object of the invention to provide a suspension system which enhances steering axle lateral stability without use of a track bar. 
     The foregoing objects are achieved as is now described. The invention provides a suspension system for the steering axle of a vehicle chassis. The suspension includes a right side air spring and a left side air spring. Both air springs are mounted above the axle and below their respective sides of the vehicle chassis for supporting the chassis. Auxiliary axle stabilizing and locating apparatus include pairs of hanger brackets depending from the vehicle chassis forward of the steering axle, one on each major side of the vehicle chassis and additional pairs of hanger brackets depending from the vehicle chassis aft of the steering axle, one on each major side of the vehicle chassis. Shackle linkages are coupled between forward hanger brackets. A right side spring half leaf and a left side spring half leaf are mounted between the frame rails and opposite ends of steering axle. Each spring half leaf is pivotally connected at one end to shackle linkages and at the opposite end is rigidly mounted on the steering axle beneath the air springs. A right side rigid arm and a left side rigid arm complete positioning of the axle. Each rigid arm is pivotally coupled at one end to hanger brackets, depending from a frame rail, and at the opposite end rigidly attached to the steering axle below an air spring. The rigid-arms are preferably connected as leading arms, but may be mounted as either leading or trailing arms, depending on the location of a steering linkage to the axle. 
     Additional effects, features and advantages will be apparent in the written description that follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a perspective view of a portion of a vehicle frame incorporating one embodiment of the invention; 
     FIG. 2 is a side elevation of the embodiment of FIG. 1; 
     FIG. 3 is a perspective view of a portion of a vehicle frame incorporating a second embodiment of the invention; and 
     FIG. 4 is a side elevation of the embodiment illustrated in FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIGS. 1 and 2, a first embodiment of a suspension system  10  in accordance with the invention is illustrated. Suspension system  10  supports vehicle chassis frame rails  11  and  12  from a steering axle  14 . Frame rails  11  and  12  are directly supported by a pair of air springs  18  and  16 , respectively. An air spring bracket  20  that helps position air spring  18  with respect to frame rail  11  is visible on the outside face of the frame rail. Steering axle  14  supports a steering linkage  30 , which acts on right side wheel (not shown) from the left side wheel  28  (shown in shadow). Steering axle  14  carries brakes (not shown) for braking rotation of wheels mounted to the axle. A steering arm  24  allows connection to a steering gear box (not shown) by either a leading or trailing linkage. Whether the linkage is leading or trailing controls which embodiment of the invention may be applied to the vehicle. The principal features of the invention are auxiliary stabilization and localization of steering axle  14 . 
     Where a leading linkage is used to connect to steering arm  24 , the embodiment of FIGS. 1 and 2 is employed. In order to avoid suspension steering it is important to maintain the steering axle  14  in a position perpendicular to frame rails  11  and  12  and to keep the axle immobilized against lateral movement. Driver control of the vehicle is helped by limiting vehicle role and front end dive on braking. Since the right side suspension components mirror the left side suspension components, only the left side suspension is discussed in detail. 
     In the first embodiment, front end braking dive is controlled by employing rigid leading arms  34  and  36  as auxiliary stabilizing elements. Application of braking to wheel  28  results in torque being applied to steering axle  14  (labeled T r  in FIG.  2 ). This force translates along rigid leading arm  34  as an upward force L to hanger  32 , which is mounted aft of steering axle  14 , counteracting front end dive. Leading arm  34  is rigidly linked to steering axle  14  between the bottom of air spring  18  and the steering axle. Leading arm  34  is pivotally coupled to hanger  32  such that hanger  32  defines an axis of rotation for steering axle  14  aft of the steering axle. In order to avoid suspension steering, the linkage to steering arm  24  must also be a leading arm arrangement. Rigid arm  34  is highly resistant to twist, and thus limits body roll of a vehicle on which it is installed. 
     Axle lateral location and stabilization are further helped by using a spring half leaf  42 , which is rigidly mounted at one end to axle  14  between the rigid leading arm  34  and spacer  70 , which are installed directly below air spring  18 . Retainers  44  lock ends of leading arm  34 , spring half leaf  42  and spacer  70  to axle  14 . The opposite end of spring half leaf  42  must have some degree of freedom of movement along the direction of elongation of frame rail  11  to avoid having an axis of rotation for axle  14  forward of hanger  32 . Accordingly, spring half leaf  42  is coupled to frame rail  11  by a pivoting connection to shackle linkages  40 , which in turn are pivotally connected to a hanger  38  mounted on frame rail  11  forward of steering axle  14 . Shackle linkages  40  swing in an arc parallel to the direction of elongation of frame rail  11 . Shackle linkages  40  may comprise a one piece shackle box or multi piece arrangements. 
     A shock absorber  22  dampens oscillations of the suspension system. Shock absorber  22  is connected between a pivot mount on frame rail  11  and a pivot mount from spacer extension  72 . The manner of use of shock absorber  22  is conventional. 
     Referring to FIGS. 3 and 4, a second embodiment of the invention is illustrated. The second embodiment is intended for use with vehicles having trailing link steering systems. The second embodiment provides no brake anti-dive advantages and is used only on vehicles that are not or cannot be equipped with a leading steering link. Like numbers refer to like components in all of the figures. 
     Again, since the right side suspension components mirror the left side suspension components, only the left side suspension is discussed in detail. In the second embodiment, rigid trailing arms  54  and  56  act as auxiliary stabilizing elements providing substantial anti-roll support for a vehicle. Trailing rigid arm  54  is rigidly linked to steering axle  14  between the bottom of air spring  18  and the steering axle. Trailing arm  54  is pivotally coupled to forward hanger  52 , such that hanger  52  defines an axis of rotation for steering axle  14  forward of the steering axle. In order to avoid suspension steering, the linkage to steering arm  24  must also be a trailing linkage. Rigid arm  54  is highly resistant to twist, and thus limits body roll of a vehicle on which it is installed. 
     Steering axle  14  lateral location and stabilization are further helped by using a spring half leaves  62  and  64 , each of which are rigidly mounted at one end to axle  14 . One end of spring half leaf  62  is fixed between the rigid leading arm  54  and spacer  70 , which is installed directly below air spring  18 . Retainers  44  lock ends of leading arm  54 , spring half leaf  62  and spacer  70  to axle  14 . The opposite end of spring half leaf  62  must have some degree of freedom of movement along the direction of elongation of frame rail  11  to avoid having an axis of rotation for axle  14  aft of hanger  52 . Accordingly, spring half leaf  62  is coupled to frame rail  11  by a pivoting connection to shackle linkages  60 , which in turn pivotally depend from an aft hanger  58  mounted on frame rail  11  aft of steering axle  14 . Shackle linkages  60  can swing in an arc parallel to the direction of elongation of frame rail  11 . 
     A shock absorber  22  dampens oscillations of the suspension system. Shock absorber  22  is connected between a pivot mount on frame rail  11  and a pivot mount on spacer extension  72 . Shock absorber  22  is conventional. 
     The invention provides an air spring suspension system with improved vehicle stability characterized by increased resistance to front end dive on braking in the preferred embodiment and improved resistance to roll in all embodiments. In the preferred embodiment, braking torque on the steering axle is transmitted along a leading arm as an upward force on the vehicle chassis. Because of the use of both trailing and leading links, the suspension system does not require a track bar to maintain lateral location of the steering axle. 
     While the invention is shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.