Abstract:
A novel arrangement of a steering axle for a land vehicle having a hydrostatic drive system, wherein a hydraulic motor assembly is directly mounted on a steerable wheel of the axle and adapted to be movable with the wheel, is disclosed. The steering axle comprises a pair of kingpin assemblies pivotally mounting steering knuckles to axle yokes. An upper kingpin assembly pivotally attaches the steering knuckle to the axle yoke, and, at the same time, provides a hydraulic swivel coupling between the wheel mounted hydraulic motor and the rest of the hydrostatic drive system of mounted on the vehicle, that prevents the bending of the hydraulic hoses conveying hydraulic fluid, by steering movements of the front steerable wheels.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a steering axle of a vehicle having a hydrostatic front wheel drive system, and more particularly to a kingpin incorporating a hydraulic swivel coupling adapted to provide a static hydraulic connection between a hydraulic motor mounted directly on a steerable wheel and a source of a pressurized hydraulic fluid mounted on a vehicle body. 
     2. Description of the Prior Art 
     Hydrostatic vehicle drive systems have been very popular and commonly used for many vehicles of the “off-highway” type, such as industrial and farming machines, or similar vehicles. Drive wheels of such vehicles are directly driven by fluid pressure actuated hydraulic motors, often mounted directly to the drive wheels, both steerable and nonsteerable. Correspondingly, the vehicles are provided with one or more sources of pressurized hydraulic fluid mounted on a vehicle body, usually in the form of hydraulic pump(s). The vehicular hydrostatic drive system is a highly complex assembly of one or more hydraulic pumps and various valves assemblies interconnected by hydraulic fluid lines. A substantial number of vehicles having the hydrostatic transmission system are provided with a front axle (seldom with a rear axle) having both steering and driving capabilities, wherein a hydraulic motor is mounted directly to the front wheels. A series of hydraulic hoses interconnect the wheel mounted hydraulic motors to the vehicle body mounted hydraulic pump. Naturally, in operation, the hoses experience numerous cycles of bending since the position of the steerable wheels and correspondingly the wheel mounted hydraulic motors change repeatedly. It is a common problem in such a system that the flexible hydraulic hoses used to supply fluid to or from the wheel motor, tend to become rigid under the influence of the pressurized hydraulic fluid, interfere with the steering and, eventually, develop a fatigue that over the period of time could lead to a damage to the hoses. 
     SUMMARY OF THE INVENTION 
     The present invention provides a hydraulic swivel coupling assembly for a steering drive axle of a vehicle having a hydrostatic drive system, wherein a hydraulic motor assembly is directly mounted on a steerable wheel of the axle and adapted to be movable with the wheel. 
     The steering drive axle of the present invention comprises a pair of kingpin assemblies pivotally mounting steering knuckles to axle yokes. An upper kingpin assembly pivotally attaches the steering knuckle to the axle yoke, and, at the same time, provides a hydraulic swivel coupling between the wheel mounted hydraulic motor and the rest of the hydrostatic drive system of mounted on the vehicle, that prevents the bending of the hydraulic hoses conveying hydraulic fluid, by steering movements of the front steerable wheels. 
     In accordance with the preferred embodiment of the present invention, the upper kingpin assembly comprises a kingpin fixedly secured to a knuckle arm, and a block manifold pivotally coupled to the kingpin and secured to the axle yoke arm. The kingpin includes a set of axial spaced hydraulic fluid passages adapted to communicate with the complimentary set of hydraulic fluid passages formed in the block manifold, at any angular position of the kingpin. 
     Therefore, the novel arrangement of the steering drive axle of the present invention prevents fatiguing and damage of the hydraulic hoses, thus substantially improving the reliability of the vehicular hydrostatic transmission. Moreover, it allows the use of less expensive hard tubes instead of the flexible hoses, thus reducing the manufacturing cost of the vehicle. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the invention will become apparent from a study of the following specification when viewed in light of the accompanying drawings, wherein: 
     FIG. 1 is a partial sectional view of one end of a front steering axle of a vehicle having a hydrostatic transmission system in accordance with the present invention; 
     FIG. 2 is a perspective view of an upper kingpin assembly in accordance with the preferred embodiment of the present invention; 
     FIG. 3 a  is a sectional view of the upper kingpin assembly taken on line A—A of FIG. 2; 
     FIG. 3 b  is a sectional view of the upper kingpin assembly taken on line B—B of FIG. 3 a;    
     FIG. 4 a  is a sectional view of a kingpin as shown in FIG. 3 a;    
     FIG. 4 b  is a sectional view of the kingpin as shown in FIG. 3 b;    
     FIG. 5 a  is a sectional view of a block manifold as shown in FIG. 3 a;    
     FIG. 5 b  is a sectional view of the block manifold as shown in FIG. 3 b.   
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The preferred embodiment of the present invention will now be described with the reference to accompanying drawings. 
     FIG. 1 of the drawings illustrates a novel arrangement of a steering axle  1  of a vehicle (not shown) equipped with a hydrostatic drive system. The steering axle of the present invention includes a rigid girder  2  provided with a pair of axle yokes  3  integrally secured at the opposite ends thereof, such as by welding. Each of said axle yokes has two bifurcated arms: an upper arm  4  and a lower arm  5 . Each axle yoke  3  is pivotally connected to a corresponding wheel knuckle  6 . Ordinarily, the knuckle  6  comprises a spindle  7  formed integrally with an upper knuckle arm  8  and a lower knuckle arm  9 . The spindle  7  is adapted to rotatably support a wheel hub  10  via a pair of roller bearings  12 . Mounted to the knuckle  6  is a hydraulic drive motor assembly  14  adapted to drive a steerable wheel (not shown) through a drive shaft  15  and a planetary gearing  16 . Typically, such drive motors are either of the axial piston type, or of the radial piston type, or of the gerotor type, although those of ordinary skill in the art will understand that any other appropriate types of the hydraulic drive motor may be employed in the present invention. 
     The hydraulic motor assembly  14  is fluidly connected to a source of pressurized hydraulic fluid, usually a single hydraulic pump assembly, mounted on a body of the vehicle (not shown) through three types of hydraulic fluid lines: pressure, return and drain lines. 
     The axle yoke  3  and the knuckle  6  are pivotally connected by means of a lower kingpin assembly  18  and an upper kingpin assembly  20 . The lower kingpin assembly  18  and the upper kingpin assembly  20  are arranged coaxially with respect to each other and are adapted to pivot about a steering axis  17 . 
     The lower kingpin assembly  18  pivotally couples the lower arm  5  of the girder yoke  3  and the lower knuckle arm  9 . It has an ordinary construction well known in the prior art and is not a significant feature of the present invention. 
     The upper kingpin assembly  20  in the steering axle  1  of the present invention, not only pivotally couples the upper arm  4  of the girder yoke  3  and the upper arm  8  of the knuckle  6 , but also functions as an integral hydraulic swivel coupling. 
     In accordance with a preferred embodiment of the present invention illustrated in FIG. 2, the upper kingpin assembly  20  comprises a kingpin  22  fixedly secured to the upper knuckle arm  8 , and a block manifold  60  pivotally coupled to the kingpin  22  and fixedly secured to the upper arm  4  of the girder yoke  3 . The kingpin  22  is provided with a set of fittings: a pressure hose fitting  56 , a return hose fitting  57  and drain hose fitting  58  adapted to secure to the kingpin  22  the pressure, return and drain hoses respectively (not shown), coming from the hydraulic drive motor assembly  14 . Likewise, the block manifold  60  is provided with a similar set of fittings: a pressure hose fitting  80 , a return hose fitting  81  and drain hose fitting  82  adapted to secure to the block manifold  60  the pressure, return and drain hoses respectively (not shown), coming from the hydraulic pump assembly (not shown). 
     The kingpin  22 , illustrated in detail in FIGS. 4 a  and  4   b , includes a an elongated body formed with a generally cylindrical first end portion  24 , a generally rectangular second end portion  26  and a generally cylindrical shank portion  28  interconnecting the first and second end portions  24  and  26 , respectively. The second end portion  26  of the kingpin  22  is provided with a flange  30  adapted for connection to the upper knuckle arm  8  by any appropriate means well known in the art, preferably by threaded fasteners such as bolts, as shown in FIG.  1 . 
     The body of the kingpin  22  is provided with three separate internal hydraulic flow passages: a pressure passage  32 , a return passage  34  and a drain passage  36 . Preferably, the passages  32 ,  34  and  36  are drilled axially down the kingpin body from an end face adjacent to the first end  24 . Upper ends of the pressure and return passages  32  and  34  respectively, are sealed by plugs  38 . 
     The second end portion  26  of the kingpin  22  is provided with a pressure port  40 , a return port  42  and a drain port  44  communicating with the pressure, return and drain ports respectively. As illustrated in FIGS. 2,  3   a  and  3   b , each of the ports  40 ,  42  and  44  is provided with the corresponding hydraulic hose fittings  56 ,  57  and  58  connecting the ports  40 ,  42  and  44  to the corresponding hydraulic fluid hoses of the hydraulic drive motor assembly  14 . 
     Furthermore, the first end portion  24  of the kingpin  22  is provided with three axially spaced annular channels: a pressure channel  48 , a return channel  50  and a drain channel  52 . Preferably, the channels  48 ,  50  and  52  are formed on an outer peripheral surface of the first end portion  24 , and are semicircular in a cross-section. Each of the channels  48 ,  50  and  52  is in fluid communication with the corresponding hydraulic fluid passage: the pressure channel  48  with the pressure passage  32 , the return channel  50  with the return passage  34  and the drain channel  52  with the drain passage  36  through a radial passage  37 . 
     Each of the annular channels  48 ,  50  and  52  of the first end portion  24  of the kingpin  22  is included between axially spaced grooves each receiving C-rings  54  sealingly engaging the inner peripheral surface  66  of the block manifold  60  and axially fluidly sealing (or separating) the channels from each other and ambient air. It will be appreciated that any other means to contain the hydraulic fluid to their respective ports, is within the scope of the present invention. 
     As illustrated in FIGS. 3 a  and  3   b , rotatably mounted on the outer peripheral surface of the first end portion  24  of the kingpin  22  coaxially with the axis  17  is the block manifold  60 . The block manifold  60 , illustrated in detail in FIGS. 5 a  and  5   b , is provided with a substantially cylindrical cavity  62  formed by a bottom surface  64  and a substantially cylindrical inner peripheral surface  66 . The cavity  62  is adapted to receive the first end portion  24  of the kingpin  22  so that a drain fluid chamber  67  is formed between the end face of the kingpin  22  adjacent to the first end portion  24  and the bottom surface  64  of the cavity  62 . Extending from the inner peripheral surface  66  are two spaced, substantially radial manifold passages. A pressure manifold passage  74  is arranged to register with the pressure channel  48  at one end and communicates with a block manifold pressure port  68  at the other end. Similarly, a return manifold passage  76  is arranged to register with the pressure channel  50  at one end and communicates with a block manifold return port  70  at the other end. A separate U-shaped drain manifold passage  78  interconnects the drain channel  52  with the drain fluid chamber  67  and communicates with a block manifold drain port  72 . Each of the manifold ports  68 ,  70  and  72  is provided with the corresponding hydraulic hose fittings  80 ,  81  and  82  connecting the ports  68 ,  72  and  72  to the corresponding hydraulic fluid hoses of the hydraulic pump assembly. 
     Alternatively, three axially spaced annular channels: the pressure channel  48 , the return channel  50  and the drain channel  52 , may be formed on the inner peripheral surface  66  of the block manifold  60 . In this case, the axial fluid passages  32 ,  34  and  36  formed in the kingpin  22 , are provided with respective communication ports at the first end portion  24  of the kingpin  22  arranged to register with the corresponding annular channels  48 ,  50  and  52  formed on the inner peripheral surface  66  of the block manifold  60 . 
     As explained above, in the steering axle arrangement of the present invention described hereinabove, the hydraulic pump assembly and the hydraulic motor assembly  14  fluidly communicate through the upper kingpin assembly  20  providing a hydraulic swivel coupling. The upper kingpin assembly  20  is connected to the hydraulic pump assembly and the hydraulic motor assemblies  14  through pressure, return and drain hydraulic fluid hoses. It will be appreciated that the kingpin assembly  20  of the present invention allows the steering knuckle  6  to freely swivel relative to the girder yoke  3  in response to steering force applied to the steering knuckle  6 , and, at the same time, provides a reliable hydraulic connection between the hydraulic motor  14  and the rest of the hydrostatic drive system mounted on the vehicle at any operating steering angle of the steerable driving wheels of the hydrostatic drive system without interfering with the steering movements of the wheels. 
     Therefore, the hydraulic swivel coupling of the present assembly represents a novel arrangement of the kingpin assembly  20  for the steering drive axle of the hydrostatic drive system and provides a static plumbing connection between the hydraulic motor  14  and the rest of the hydrostatic drive system mounted on the vehicle that prevents fatiguing and damage of the hydraulic hoses and allows using less expensive hard tubes instead of the flexible hoses. 
     The foregoing description of the preferred embodiments of the present invention has been presented for the purpose of illustration in accordance with the provisions of the Patent Statutes. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obvious modifications or variations are possible in light of the above teachings. The embodiments disclosed hereinabove were chosen in order to best illustrate the principles of the present invention and its practical application to thereby enable those of ordinary skill in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated, as long as the principles described herein are followed. Thus, changes can be made in the above-described invention without departing from the intent and scope thereof. It is also intended that the scope of the present invention be defined by the claims appended thereto.