Abstract:
The present invention is a self-contained, low cost and robust axle scale for weighing the load on a vehicle axle comprises a pneumatically supplied axle transmitter assembly capable of gauging the vertical displacement of the axle relative to the vehicle frame resulting from the compression of the axle suspension while bearing a cargo load wherein the axle transmitter assembly provides a pneumatic pressure output in proportion to the axle load and is communicated to an operator display pressure gauge appropriately scaled to indicate the load. The axle transmitter assembly comprises a self-returning variable pressure valve having a rotatable activator with an actuator lever arm perpendicularly fixed to the rotatable activator. The axle transmitter assembly is mounted on the vehicle frame such that the actuator lever arm rests on the axle. The pneumatic supply is drawn from the compressed air reservoir tank typically found on vehicles with pneumatic brakes such as trucks.

Description:
FIELD OF THE INVENTION 
   The present invention relates to axle weigh scales. More particularly, this invention is directed to a self contained axle load scale mounted on a vehicle used principally in the trucking industry for measuring the static load on a truck axle. 
   BACKGROUND OF THE INVENTION 
   The trucking industry is required to comply with regulations limiting the total weight and per axle load distribution imparted by a truck, including any cargo load, to a road surface. Typically a truck is loaded with cargo and then driven onto a weigh scale to measure the weight of each axle and the total combined weight. 
   Regulations specify the maximum total allowable weight permitted for a truck and also the maximum allowable weight per axle. Consequently, the trucker typically estimates the axle loads at time of loading the truck and drives the loaded to truck to a weigh scale facility prior to embarkation. The total weight of the truck load may be less then maximum total load limits while the distribution of the load among the axles may result in particular axles bearing excessive loads. Consequently efficient loading of the truck is a useful skill as adjustments to the distribution of the load are often time consuming and can be difficult once the truck is fully loaded. 
   The truck loading process has heretofore been guided primarily by experience and skill so as to distribute the load along a truck trailer or bed such that the total truck and axle weight regulations are satisfied while also maximizing the amount of cargo. Ideally, knowledge of the axle weights during the loading of the truck would facilitate the full loading of the truck so as to satisfy both objectives without the necessity of driving the truck to weigh scale facilities. Portable drive-on truck scales are sometimes carried with the trucks to facilitate axle load measurements at a loading site; however, this solution is usually not practical because of the inconvenience, size, weight and cost of the scales. Further, portable weigh scales when positioned on a surface present a vertical height offset such that when one set of wheels of a tandem axle are driven on to the scale, the load measurements must be corrected as the suspension springs of the measured wheel set are compressed more than the adjacent axle springs. Consequently, to obtain an accurate total weight of the vehicle one must utilize multiple portable axle scales located under each wheel set making portable scales impracticable for accurate on-site load measurement. 
   Alternatively, a dedicated apparatus mounted to each axle for load measurement eliminates the need to drive to a truck weigh scale facility. Incorporating a weigh scale apparatus permanently into a truck presents significant challenges. For a device to be mounted on the truck, the load measurement is accomplished by a transducer placed between the truck frame and the axle. For example, a transducer measuring load directly, such as a strain gauge, may be placed between the frame and the axle assembly. Alternatively, a linear displacement transducer may be positioned between the truck frame and the axle to measure the displacement of the frame relative to the undercarriage to measure the suspension compression. In either of these examples, electronic controllers are typically required to convert the transducer output signal into axle load information. The high capital cost of such controllers is often difficult to justify for dedicated installation. Additionally, for systems that are permanently mounted to the truck, the load transducer should be capable of tolerating both the large dynamic load changes and shocks presented by normal driving while also having sufficient sensitivity and capability to perform reliably and repeatability under the important static load conditions during truck cargo loading axle load measurement. Further, the harsh operating environment found between the truck frame and the road surface is particularly challenging for sensitive electronic transducers and the associated wiring and electronic controls. Road salts are aggressively corrosive to electronic components and wiring. Road debris requires transducers and sensors to be resistant to impact and particulate features. 
   Still other methods of axle scale load measurement include the incorporation of pneumatic bags in the suspension system wherein the air pressure in the bag increases with the compression of the bag in proportion to the axle loads. Alternatively, the pneumatic bag forms a portion of the shock absorbing or leveling. These measurement devices are typically integrated into the undercarriage suspension. 
   Accurate measurement of the axle loads, prior to the present invention, has required load measuring devices typically placed between the truck frame and the axle assemblies so as to measure the weight of a load and a truck frame. Load cells and other pressure measuring transmitters are typically mounted between the suspension and the axle. These systems are comprised of a transmitter element in electronic communication with a computing device and a data display element. The transmitters are exposed to high dynamic load changes during normal driving necessitating robust construction to achieve acceptable equipment reliability. Further, exposure to road debris, corrosives, oil and other hazards create a harsh operating environment especially for electronic components and wiring. Consequently economic and reliability constraints discourage the installation of axle load measuring devices. 
   What is needed is an improved truck axle scale being of low cost, simple installation, and incorporating robust engineering features capable of operation in environments present in and around the axle and carriage of a truck. 
   SUMMARY OF THE INVENTION 
   Accordingly, the present invention is directed to axle scale devices and, more specifically, to a self contained truck axle scale mountable on a truck or other vehicle being of robust design and low cost permitting permanent mounting to a truck thereby substantially obviating one or more of the problems due to the limitations and disadvantages of the related art. 
   The axle scale of this invention comprises a pneumatically supplied axle transmitter assembly capable of providing a pneumatic pressure output in proportion to the increased mechanical compression of the axle suspension springs as measured by the vertical linear displacement when gauged between the vehicle frame and the axle resulting from a cargo load. An operator display gauge, being in direct pneumatic communication with the output of the axle transmitter assembly and scaled accordingly to convert the pressure to an equivalent total axle load, presents the resulting load information to the operator. The axle transmitter assembly provides no or low pneumatic output pressure when no cargo load is present and increases as cargo load compresses the suspension springs. The operator display gauge is therefore scaled to reflect the total axle load presented to a road surface by indicating the axle load absent cargo when there is no or low pneumatic output pressure from the axle transmitter assembly. 
   The axle transmitter assembly comprises a variable pressure pneumatic valve, having a rotatable activator, capable of providing a pneumatic pressure to the operator display pressure gauge wherein the variable pressure pneumatic valve is activated in proportion to the load on an axle by means of an actuator lever, having proximate and distal ends, with the proximate end fixed perpendicularly to the rotatable activator member of the pneumatic valve and the distal end of the actuator lever in contact with the truck axle thereby providing rotation to the pneumatic valve in proportion to the vertical linear displacement of the axle relative to the truck frame when the truck is loaded with cargo. 
   An axle transmitter assembly is mounted to the truck frame for each axle with the actuator lever arm positioned to rest on the respective undercarriage axle assembly. Pneumatic pressure is supplied to the input of the axle scale transmitter valve and the output is communicated to an operator display gauge being a pressure gauge with markings corresponding to the load applied to the axle for given pressures. The loads on each axle are measured individually to determine the load distribution and totaled to determine the total weight of the vehicle and cargo load. 
   The linear displacement as determined by the change in distance between a reference point on the truck frame and the undercarriage is gauged by the resulting degree of rotation of the actuator of the variable pressure valve. The degree of rotation is therefore directly and linearly proportional to the linear displacement. In turn, the output port of the variable pressure valve presents a pneumatic pressure according to the degree of rotation of the rotatable activator. 
   As the axle transmitter assembly is pneumatically powered, the apparatus may be conveniently supplied by the compressed air reservoir present on vehicles with air braking system thereby eliminating the need for a separate, dedicated pneumatic supply. 
   An objective of the present invention is to minimize the cost of the apparatus. As such, the required pneumatic supply is alternatively drawn from the pneumatic braking supply already present on most trucks. 
   Still another objective to provide a robust design is accomplished by utilizing pneumatic pressure to communicate the axle load information. As such, plastic pneumatic lines may be utilized which are inexpensive, reliable and resistant to corrosion and road debris. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of this specification illustrate embodiments of the invention and, together with the description, serve to explain the features, advantages, and principles of the invention. 
       FIG. 1  is a side plan view of a truck, having been fitted with and in accordance with the present invention, with a broken away area to show the activating toggle switches and operator display gauges, for displaying axle loads, on the truck dashboard, the air tank and axle scale transmitter valve are in dotted outline. 
       FIG. 2  is a plan view of the dashboard taken on line  2 - 2  of  FIG. 1  showing the operator display gauges and the activator switches. 
       FIG. 3  is a front plan view of the present invention with the axle scale transmitter valve mounted on the frame of the truck and gauging the front axle. 
       FIG. 4  is a side view of the axle scale transmitter valve taken on the line  4 - 4  of  FIG. 3  drawn in larger scale with a broken away area to show the o-ring seal. 
       FIG. 5  is an enlarged view of the o-ring area circled at arrow  5  in  FIG. 4 . 
       FIG. 6  is a rear view of the axle scale transmitter valve taken on line  6 - 6  of  FIG. 4 . 
       FIG. 7  is a front view of the axle scale transmitter valve mounted on the frame of the truck with actuator lever resting on and gauging the rear axle with the rear end plate mounted on the differential. 
       FIG. 8  is a view of an alternate mounting of the axle scale transmitter of the present invention wherein the transmitter and mounting plate are clamped to a tubular element of the truck frame and the actuator lever arm is resting on and gauging a truck axle assembly. 
       FIG. 9  is a pneumatic schematic of the axle scale according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Although particular embodiments of the invention have been described in detail for purposes of illustration, various modifications may be made without departing from the spirit and scope of the invention. Accordingly, the invention is not to be limited except as by the appended claims. Referring now in greater detail to the various figures of the drawings wherein like reference characters refer to like parts, there is shown in  FIG. 1 , a new type of self contained axle scale used in the trucking industry wherein an axle scale transmitter assembly  10  is mounted to the truck frame  18  so as to gauge the vertical displacement of an axle  22  resulting from a cargo loaded on the truck  72 , being supplied by a pneumatic pressure from the compressed air reservoir tank  60 , and providing an output pressure to an operator display gauge, two shown at  40  and  42 , mounted on the dashboard  48  of the truck  72  and activated by actuator switches  44  and  46 , wherein the gauge presents a reading associated with the load on the axle  22 . 
     FIG. 2 , taken along line  2 - 2  of  FIG. 1 , of the truck dashboard  48  shows the operator display gauges  40  and  42  conveniently mounted for viewing with activation switches  44  and  46  within close reach. The operator display gauges are responsive to pneumatic pressure and are preferably an analog display type gauge; however, digital display type gauges are also suitable. 
   Referring to  FIG. 3 , the axle transmitter assembly  10  comprises a variable pressure pneumatic valve  14  having a rotatable activator  50  with the proximate end of actuator lever arm  12  fixed perpendicularly to the rotatable activator  50  and a clevis  28  retaining roller  30  fixed to the distal end of the actuator lever arm  12 . The axle transmitter assembly  10  further comprises a means for mounting to the vehicle frame  18  wherein the means is frame mounting plate  16 , also shown in  FIG. 3 , attached to the frame  18  with mounting plate bolts  24  and with the variable pressure pneumatic valve  14  mounted to the mounting plate  16  with valve mounting bolts  58 . The axle transmitter assembly  10  is fixed to the vehicle frame  18  in a position such that the roller  30  at the distal end of the actuator lever arm  12  rests on the vehicle axle  22 . 
   Leaf spring suspensions commonly used in trucks and truck trailers deflect in an approximately linear manner and in proportion to the load for loads within the capacity limits of the truck. The leaf spring assembly  20 , shown in  FIG. 3 , typically provides the means for mounting the axle  22  to the truck frame  18  and assumes the load applied to the axle  22 . The amount of deflection of the suspension is also in proportion to the vertical displacement of the truck frame  18  relative to the axle  22 . Other suspension systems exhibit similar vertical displacements in proportion to the load on the axle. 
   The preferred embodiment of the present invention gauges the vertical displacement of the axle relative to the truck frame using the variable pressure pneumatic valve  14  wherein the valve  14  presents a pneumatic pressure at the valve output proportional to the rotational position of the valve activator  50 . Such pneumatic valves are known in the industry and are often used as a brake hand valve for truck pneumatic braking systems. Experiments have shown in the present invention that an industry standard Midland RN-0542 self-returning pneumatic valve exhibits the required functionality although others may be used. 
   Referring to  FIG. 4 , showing the axle transmitter assembly  10  with variable pressure valve  14  fixed to mounting plate  16  by valve mounting bolts  58  with the valve rotatable activator  50  protruding through the mounting plate  16  and actuator lever arm  12  extending perpendicularly from the rotatable activator  50 . As also shown in  FIG. 5 , the variable pressure valve  14  is adapted to retain o-ring  32  for sealing the rotatable activator  50  mechanism from debris. The axle transmitter assembly  10  is mounted to the truck frame  18  with mounting bolts  24 . 
     FIG. 6 , showing a rear view of the transmitter assembly  10 , illustrates the rear of the variable pressure valve  14  fixed to the mounting plate  16 . The valve  14  provides a pneumatic supply inlet port  56 , a pneumatic output port  52 , an exhaust port  54  and includes an axially secured rotatable activator  50  with integral shaft wherein the pneumatic pressure presented at the output port  52  varies in direct proportion to the degree of rotation of the actuator shaft provided a pneumatic supply pressure is present at the supply inlet port  56 . The activator  50  rotates from a rest position wherein the output port pressure is or near 0 PSI, the unactuated state, to a fully activated position, typically 50 degrees, wherein the output port  52  pressure is or near the pneumatic pressure supplied at the inlet port  56 . The output pressure thereby varies proportionally with the rotation of the activator  50  from 0 PSI to the supply pressure. The pressure is created at the output port  52  by diverting air from the supply port  56  to the output port  52  until the output port  52  is at a pressure associated with the rotational position of the activator  50  shaft. The output port  52  is in pneumatic communication with a pressure gauge  40  by means of a pneumatic line. Pressurized air is supplied by the valve to pressurize the line and the pressure gauge until the required pressure corresponding to the degree of rotation of the activator  50  shaft is established. In this manner the gauge  40  reading is also in direct proportion to the pressure supplied by the valve  14  and therefore in direct relation to the rotational position of the activator  50  shaft of the valve  14 . As the activator  50  shaft is rotated away from the rest position, the pressure supplied to the gauge  40  increases. Conversely, as the activator  50  shaft is rotated back towards the rest position, the pressure supplied to the gauge  40  decrease as the valve  14  vents air to the exhaust port  54 . 
   Referring again to  FIG. 3 , the actuator lever arm  12  having a proximate and distal end is perpendicularly fixed at the proximal end to the activator  50  shaft with the distal end of the actuator lever arm  12  is positioned proximate to the axle  22  to be measured. The transmitter valve assembly is attached to the truck frame  18  and preferably positioned relative to the truck frame  18  such that the longitudinal portion of the rotatable activator  50  shaft is approximately parallel to the horizontal plane of the truck frame to maximize the rotation of the activator  50  shaft for any given vertical displacement. The transmitter assembly is additionally positioned such that the distal end of the actuator lever arm  12  contacts the truck axle  22  and rests on the truck axle  22  as the axle moves up or down relative to the truck frame  18  such that an upward motion of the truck axle  22  produces a rotation of the actuator  50  shaft in the direction of increasing the valve  14  output pressure. In the preferred embodiment, a variable pneumatic valve  14  of the transmitter assembly further comprises a spring mechanism to provide a force to return the rotatable activator  50  to the rest position thereby providing a means for the distal end of the actuator lever arm  12  to remain in contact with the truck axle  22  as the axle  22  moves up and down relative to the truck frame  18 . The Midland RN-0542 valve, being a self-returning valve, provides a spring mechanism for returning the rotatable activator  50 . 
   In the present invention, the length of the actuator lever arm  12  is conveniently adjusted to provide a relationship of 1 P.S.I. of pneumatic pressure presented by the transmitter assembly for every 1000 lbs of axle load. As the length of the actuator arm  12  defines the scaling of the invention, the length of the actuator lever arm  12  is determined by loading a particular truck tandem axle to 34,000 lbs and then adjusting the length of the actuator such that the gauge is presented with 34 P.S.I. of pneumatic pressure. Current trucking regulations limit tandem axle loads to 34,000 lbs, 20,000 lbs. for single axles, and 12,000 lbs. for the tractor front axles. The same technique is used when other axle weight limits other are required. Shortening the actuator lever arm  12  length increases the scale factor of the displacement of the axle  22  relative to the pneumatic pressure at the gauge  40 . For most truck axle suspensions, both tandem and single axles, the vertical displacement relative to the truck frame due to the compression of a fully loaded truck has been determined to be in the approximate range of 1.25 to 1.75 inches thereby requiring an actuator lever length of approximately 5.25 inches. This actuator lever arm  12  length translates into approximately a 10 degree rotation of the proportional valve  14  and hence a 34 P.S.I. pneumatic pressure for tandem axles is presented to the operator gauge  40 . These dimensions will vary depending upon the design of the truck upon which the invention is installed and the current trucking regulation load limits. 
   For tandem axles, calibration of the length of the actuator lever arm  12  should be performed on level ground as differences in ground level between the axles will load the axles differently resulting in differing spring compressions on each axle. 
   As the maximum compression of the suspension springs is small in relation to the maximum design displacement for axle suspensions, spring suspensions have been determined to respond linearly over the full load range for the truck when the truck is static thereby providing linearity of the present invention over the full load range. Experiments have shown that for a 34,000 lb. tandem axle load or a 20,000 lb. single axle load, undercarriage spring compression for single, three and multi-stacked assemblies generally produce a linear displacement of about 1.25 inches. When using the afore-identified Midland valve the actuator lever arm should be approximately 5.25 inches. 
   The clevis  28  with roller  30  is optional however a roller presented to the surface of the undercarriage minimizes the wear of the actuator lever arm  12  and axle  22  casing. As  FIG. 7  shows, a strike plate  26  may also be used to provide a contact surface on an axle assembly particularly when irregularly shaped undercarriage features are encountered. 
     FIG. 8  illustrates an embodiment wherein no clevis with roller is utilized. This embodiment is useful when mounting the axle transmitter assembly  10  to vehicles with round undercarriage features such as the tubular axle at  38 . Also note that a variety of embodiments of the mounting plate  16  may be engineered so as to accommodate mounting requirements. In  FIG. 8 , the mounting plate  16  is engineered to retain u-bolts  34  for mounting the axle transmitter assembly  10  on tubular structures  36  of a vehicle frame. 
     FIG. 9  shows a preferred embodiment of the pneumatic schematic with two axle scale installations. The pneumatic supply is preferably provided by the truck compressed air reservoir tank  60  used for the braking system although any pneumatic supply may be used. The compresses air reservoir tank  60  is pressurized by the engine air compressor  62 . A pneumatic line may be connected to the compressed air reservoir  60  and routed to the supply inlet of the variable pressure valve  14  of the axle scale transmitter assembly  10 . However, although not required for the essential operation of the axle scale, the inlet of a low pressure cut off valve  64  is preferably in direct pneumatic communications with the truck compressed air reservoir  60  as the reservoir is typically also used for supplying the braking system. The cut off valve prevents failure of the vehicle braking system in the event of leakage from the axle scale. In the embodiment, shown in  FIG. 9 , the outlet of the low pressure cut off valve  64  is in direct pneumatic communication with the supply inlet port of the variable pressure valve  14  wherein the low pressure cut off valve  64  further incorporates a pressure regulator function for purposes of improving the accuracy and stability of the scale readings. Optionally the valve, still further, incorporates a filter to protect the axle scale from debris from the compressed air supply. 
   Also in  FIG. 9 , the exhaust port  54  of the variable pressure valve  14  vents to the atmosphere preferably through a pneumatic filter thereby preventing debris from entering the valve. Alternatively the exhaust port  54  of the valve is connected to a pneumatic line that is in direct pneumatic communication with the atmosphere at the distal end with the distal end being conveniently fastened to the truck frame in an area less inclined to accumulate debris and where the venting air may be exhausted. 
   Further in  FIG. 9 , for transmitter assemblies incorporating a variable pressure valve  14  wherein the output port is restricted to a one way flow, the pressure at the output port is not bled down internally to lower pressures. Therefore, in a preferred embodiment, the outlet port of the variable pressure valve  14  is in direct pneumatic communication with the inlet port of a 3-way pneumatic valve  70  by means of pneumatic line at  74 . The 3-way pneumatic valve  70  is used to vent the pneumatic lines connecting the variable pressure valve  14  with the display gauge  40  and  42 . The 3-way valve  70  has an inlet port, a first outlet port and a second outlet port and is so engineered as to provide selectable configurations wherein a first configuration is the closed position, a second configuration is the vent position, and a third configuration is the open position. In the closed position, there is no communication between any port. The second configuration provides direct communication between all ports. The third configuration provides direct communication between the inlet port and the second outlet port with the first outlet port shut. 
   In this preferred embodiment, the outlet port of the axle scale transmitter valve is in direct communication with the inlet port of the selectable 3-way valve  70 , the first outlet port  76  is vented to atmosphere, and the second outlet port is in direct pneumatic communication with the display gauge  40 . The apparatus is considered to be in the off mode when the 3-way valve is in the closed or first configuration position. In the off mode, no pneumatic communication is present between any ports thereby presenting no pressure to the operator display gauge. In this mode the gauge is protected from pressure transients induced by high dynamic loads as experienced during driving. To activate the system, the operator adjusts the 3-way valve  70  from the first to configuration to the third configuration wherein the valve necessarily, but momentarily is in the second configuration wherein the pneumatic lines connected to the 3-way valve are vented to atmosphere thereby insuring that no pressure exists in the lines which may yield an erroneous reading on the display gauge. When in the on mode, as when the 3-way valve is in the third configuration, the axle scale transmitter valve output is in pneumatic communication with the display gauge and the gauge is pressurized to the output pressure of the transmitter valve. 
   For embodiments incorporating variable pressure valves that vent internally, the 3-way valve  70  is optional; however presence of the 3-way valve  70  significantly improves the reliability of the system. Without the 3-way valve  70  the operator display gauge  40  is continuously supplied with compressed air from the variable pressure valve  14  during operation of the truck. When the truck is in motion, the dynamic axle loads are displayed on the gauge  40  resulting in shock to the gauge mechanism. 
   In the preferred embodiment, the 3-way valve is mechanically actuated and manually operated; however, as illustrated in  FIG. 9 , an electronic solenoid actuator  78  operated 3-way valve may optionally used in the alternative so as to provide remote electrical activation for convenience as may be required for particular installations.