Patent Publication Number: US-2012024081-A1

Title: Trailer hitch monitoring apparatus and method

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of application Ser. No. 61/368,739 filed Jul. 29, 2010. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     An assembly for monitoring the trailer hitch loads of a tow vehicle is provided in addition to a trailer hitch monitoring apparatus and a method for monitoring a trailer hitch assembly. 
     2. Description of the Prior Art 
     Various assemblies for monitoring trailer hitch loads are well known in the art. An example of such assemblies are disclosed in U.S. Pat. No. 6,053,521 to Schertler and U.S. Pat. No. 6,253,626 to Shoberg et al. 
     Schertler discloses an assembly for monitoring the trailer hitch loads of a tow vehicle including a hitch support for attachment with the tow vehicle. Schertler also discloses a hitch including a hitch base having a hitch base radius. The hitch also includes a hitch ball disposed on and above the hitch base and a lug. The lug has a cylindrical shape and extends downwardly from the hitch base. The lug has threads and a lug radius that is less than the hitch base radius. A nut having threads is disclosed for threadedly engaging the lug of the hitch to couple the hitch and the hitch support. 
     Shoberg et al. discloses an instrument spacer disposed between the hitch base and the hitch support. The instrument spacer includes a top surface abutting the hitch base and a bottom surface abutting the hitch support. The instrument spacer defines a bore. At least one strain gauge is disposed on the instrument spacer generating a resistance change for measuring forces applied to the instrument spacer. A data acquisition system electrically connected to the at least one strain gauge is provided. The data acquisition system includes a Wheatstone bridge circuit measuring the resistance change of the at least one strain gauge and generating a force measurement. 
     Wireless transmitters, receivers, and simple user information displays are also well known in the art. This includes a transmitter electrically connected to the Wheatstone bridge circuit for wirelessly transmitting the force measurement, a receiver base including a receiver receiving the force measurement from the transmitter, and a user information display electrically connected to the receiver and graphically presenting the force measurement. 
     In view of the prior art referenced herein, various methods for monitoring a trailer hitch assembly are also known in the art. The known methods include monitoring a trailer hitch assembly including a hitch support and a hitch. The hitch includes a hitch base having a hitch base radius. The hitch also includes a lug extending from the hitch base. The assembly also includes an instrument spacer disposed between the hitch base and the hitch support. The instrument spacer defines a cylindrical bore. The assembly further includes at least one strain gauge disposed on the instrument spacer generating a resistance change and a user information display. The known methods include the steps of measuring the resistance change of the at least one strain gauge using a Wheatstone bridge circuit, calculating a resultant force value in response to measuring the resistance change of the least one strain gauge, and displaying at least one of the resultant force value on the user information display. 
     SUMMARY OF THE INVENTION 
     The subject invention provides for the assembly for monitoring the trailer hitch loads of a tow vehicle described above further comprising at least one strain gauge disposed on the instrument spacer at a radial distance from the central bore axis being less than or equal to the hitch base radius and greater than or equal to the bore radius. 
     The subject invention also provides a method for monitoring a trailer hitch assembly described above further comprising the steps of positioning the at least one strain gauge on the instrument spacer at a radial distance from the central bore axis being less than or equal to the hitch base radius and greater than or equal to the bore radius and calculating a torque value in response to measuring the resistance change of the least one strain gauge. 
     ADVANTAGES OF THE INVENTION 
     The subject invention provides several advantages. Unlike prior art designs the subject invention allows for detection of proper torque applied to the hitch and nut during hitch ball installation. This is useful because proper installation of the hitch ball is critical for safe towing. The inadequate application of torque to the nut during installation may enable the nut to work loose during towing causing catastrophic failure of the trailer hitch. The arrangement of the strain gauges pursuant to the subject invention allows for detection of correct installation torque on the hitch and the nut and can provide a warning when the hitch has not been installed properly. The subject invention further provides a warning when the nut has worked itself loose or when the trailer hitch assembly has been tampered with. 
     The subject invention also provides for the detection of tongue weight, towing load capacity, and secure hitch ball to trailer coupling. Accordingly, the subject invention detects unsafe towing conditions and may warn the user before a catastrophic event occurs. The towing load on a vehicle is a function of many factors including but not limited to vehicle speed, road grade, road conditions, wind direction, wind magnitude, tire inflation pressure, and drag forces. When the towing load becomes too great, damage to the tow vehicle can occur. Additionally, overloading a trailer can cause unsafe towing conditions and may lead to failure of the trailer hitch assembly. The subject invention continuously monitors the trailer hitch assembly and initiates a warning where unsafe conditions have been reached. The subject invention can also be used as a theft detection system by detecting slight changes in trailer load and activating a security alarm to ward off potential tampering and theft. 
     Unlike prior art designs, the subject invention can also be easily installed on existing trailer hitch hardware. Where prior art designs require purchase of new trailer hitch receivers, hitch balls, and hitch supports, the instrument spacer of the subject invention simply mounts to the existing hitch support using the existing hitch ball, lug, and nut for attachment. Thus, the subject invention may be easily retro-fit to existing trailer hitch hardware at minimal cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
         FIG. 1  is an elevation view of the hitch of the subject invention illustrating the forces applied to the hitch during acceleration and deceleration, 
         FIG. 2  is a perspective view of hitch of the subject invention illustrating the area of force transference between the hitch base and the instrument spacer, 
         FIG. 3  is a side elevation view of the hitch of the subject invention illustrating the forces acting on the hitch, 
         FIG. 4  is a side elevation view of the hitch of the subject invention illustrating the forces acting on the hitch during acceleration, 
         FIG. 5  is a side elevation view of the hitch of the subject invention illustrating the forces acting on the hitch during deceleration, 
         FIG. 6  is a top view of the instrument spacer of the subject invention illustrating the area of force application on the instrument spacer, 
         FIG. 7  is a schematic of the data acquisition system of the subject invention, 
         FIG. 8  is a top view of the instrument spacer of the subject invention illustrating arrangements of the at least one strain gauge on the instrument spacer, 
         FIG. 9  is a perspective view of the instrument spacer of the subject invention illustrating arrangements of the at least one strain gauge on the instrument spacer, 
         FIG. 10  is an elevation view of the hitch assembly of the subject invention illustrating the x-axis and the y-axis and the z-axis, 
         FIG. 11  is an exploded view of trailer hitch assembly of the subject invention, 
         FIG. 12  is a front elevation view of the receiver base and the user information display of the subject invention, and 
         FIG. 13  is a perspective view of trailer hitch assembly of the subject invention. 
     
    
    
     DETAILED DESCRIPTION OF THE ENABLING EMBODIMENTS 
     Referring to the Figures, wherein like numerals indicate corresponding parts throughout the several views, an assembly  20  for monitoring the trailer hitch loads of a tow vehicle is provided. 
     The assembly  20  includes a hitch support  22  attached to the tow vehicle. The hitch support  22  may be integral with the vehicle or a receiver type trailer hitch which allows for the removal of the hitch support  22  from the tow vehicle. A hitch  24  coupled to the hitch support  22  is also provided. The hitch  24  includes a hitch base  26  and a hitch ball  28  disposed on and above the hitch base  26 . The hitch base  26  has a hitch base radius R H . A lug  30  having a cylindrical shape extends downwardly from the hitch base  26 . The lug  30  has threads and a lug radius R L  that is less than the hitch base radius R H . A nut  32  having threads threadedly engages the lug  30  of the hitch  24  to couple the hitch  20  and the hitch support  22 . Various size hitch balls  28  may be employed to assure proper coupling with a trailer. Some common hitch ball sizes includes 1⅞ inches, 50 millimeters (1.97 inches) (ISO standard), 2 inches, and 2 5/16 inches. 
     An instrument spacer  34  is disposed between the hitch base  26  and the hitch support  22 . The instrument spacer  34  includes a fore end  36  facing the tow vehicle and an aft end  38  opposite the fore end  36 . The instrument spacer  34  further includes a pair of sides  40  spaced between the fore end  36  and the aft end  38 . The instrument spacer  34  has a top surface  42  abutting the hitch base  26 . The top surface  42  extends between the fore end  36 , the aft end  38 , and the sides  40 . The instrument spacer  34  also has a bottom surface  44  abutting the hitch support  22 . The bottom surface  44  extends between the fore end  36 , the aft end  38 , and the sides  40 . The instrument spacer  34  defines a cylindrical bore  46  adjacent the aft end  38 . The cylindrical bore  46  extends along a central bore axis A from the top surface  42  of the instrument spacer  34  to the bottom surface  44  of the instrument spacer  34 . The cylindrical bore  46  has a bore face  48  of cylindrical shape and a bore radius R B  extending between the bore face  48  and the central bore axis A. The bore radius R B  is less than the hitch base  26  radius. The cylindrical bore  46  receives the lug  30  of the hitch  24 . 
     The assembly  20  further includes at least one strain gauge  50  disposed on the instrument spacer  34 . More specifically, the at least one strain gauge  50  is disposed on the instrument spacer  34  at a radial distance D from the central bore axis A that is less than or equal to the hitch base radius R H  and greater than or equal to the bore radius R B . While the at least one strain gauge  50  may be placed anywhere where the radial distance D between it and the central bore axis A is less than or equal to the hitch base radius R H  and greater than or equal to the bore radius R B , there are a number of preferred arrangements. According to one arrangement, the at least one strain gauge  50  may be disposed on the bore face  48 . According to another arrangement, the at least one strain gauge  50  may be disposed on the aft end  38  of the instrument spacer  34 . 
     The at least one strain gauge  50  may also be a plurality of strain gauges  50 . Any number of strain gauges  50  is envisioned but the plurality of strain gauges may include a first strain gauge  50  and a second strain gauge  52 . While any individual strain gauge  50  of the plurality of strain gauges may be placed anywhere where the radial distance D between it and the central bore axis A is less than or equal to the hitch base radius R H  and greater than or equal to the bore radius R B , there are a number of preferred arrangements. According to one arrangement, the first strain gauge  50  may be disposed on the bore face  48  and the second strain gauge  52  may be disposed on the aft end  38  of the instrument spacer  34 . Under this arrangement, the first strain gauge  50  may be disposed on the bore face  48  adjacent the aft end  38  of the instrument spacer  34 . Alternatively, the first strain gauge  50  may be disposed on the bore face  48  nearest the aft end  38  of said instrument spacer  34 . According to another arrangement, both the first strain gauge  50  and the second strain gauge  52  may be disposed on the bore face  48 . Under this arrangement, both the first strain gauge  50  and the second strain gauge  52  may be disposed on the bore face  48  adjacent the aft end  38  of the instrument spacer  34 . Alternatively, both the first strain gauge  50  and the second strain gauge  52  may be disposed on the bore face  48  nearest the fore end  36  of the instrument spacer  34 . According to another arrangement, both the first strain gauge  50  and the second strain gauge  52  may be disposed on the aft end  38  of the instrument spacer  34 . 
     The at least one strain gauge  50  is employed accordingly to these various arrangements to measure strain applied to the instrument spacer  34  by the hitch  24  as the hitch  24  is acted on by various forces. These forces can include a tongue load force F L , a towing force F T , a resultant force F R , and a torque value T. The tongue load force F L  is the vertical force resulting from a moment imbalance due to the weight of the trailer as well as the weight of the load on the trailer relative to the position of the trailer axle(s). This is commonly referred to as tongue weight. The towing force F T  is the horizontal force resulting from movement of the trailer relative to the tow vehicle. Accordingly, the magnitude and direction of towing force F T  varies depending on whether the trailer is accelerating or decelerating (braking). The resultant force F R  is a sum of the tongue load force F L , a towing force F T  and represents the total force acting on the hitch  24  at any given time. The torque value T is a measurement of the moment (twisting force about the central bore axis) applied to the hitch  24 . It is useful in measuring whether the hitch  24  has been properly secured to the hitch support  22  (that the nut  32  has been properly tightened about the lug  30 ). 
     The at least one strain gauge  50  measures the strain applied to the instrument spacer  34  by generating a resistance change in response to the strain applied to the at least one strain gauge  50 . More specifically, the resistance of the at least one strain gauge  50  increase when the at least one strain gauge  50  is placed under tension. Likewise, the resistance of the at least one strain gauge  50  decreases when the at least one strain gauge  50  is placed under compression. The at least one strain gauge  50  is electrically connected to a data acquisition system  54 . The data acquisition system  54  may include one or more Wheatstone bridge circuits  56 . The one or more Wheatstone bridge circuits  56  measure the resistance change of the at least one strain gauge  50  and generate a force measurement. The data acquisition system  54  may also include a transmitter  58  electrically connected to the one or more Wheatstone bridge circuits  56 . The transmitter  58  then wirelessly transmits the force measurement received from the one or more Wheatstone bridge circuits  56 . 
     A receiver base  60  includes a receiver  62  receiving the force measurement wirelessly transmitted by the transmitter  58 . The receiver base  60  also may include a user information display  64  electrically connected to the receiver  62 . The user information display  64  graphically presents the force measurement. The user information display  64  may or may not be attached to the tow vehicle. The user information display  64  may include light arrays indicating the magnitude of the tongue load and the tow capacity measured. The user information display  64  may also include a light array indicating whether the instrument spacer  34  and the hitch  24  is properly installed (that the nut  32  is properly tightened to the lug  30 ). The user information display  64  may also include a light array indicating whether the hitch  24  is loaded (non-zero tongue load force F L  indicating that the trailer is coupled to the hitch ball  28 ). Of course while the subject invention envisions wireless communication between the data acquisition system  54  and the user information display  64 , the transmitter  58  and receiver  62  may be eliminating and replaced with wired electrical connections to facilitate communication between the data acquisition system  54  and the user information display  64 . 
     The assembly  20  may include an accelerometer  66  electrically connected to the data acquisition system  54 . The accelerometer  66  generates an acceleration measurement and relays the acceleration measurement to the data acquisition system  54  The towed mass value, the trailer sway value, and the suspension oscillation value can be used in the control of the braking system and suspension system of the tow vehicle and the trailer. The towed mass value, the trailer sway value, and the suspension oscillation value can also be used in the control of the transmission and throttle of the tow vehicle. The accelerometer  66  may take many forms but may be a three axis accelerometer  66  providing acceleration measurement along an x-axis X, a y-axis Y, and a z-axis Z. The acceleration measurement along the x-axis X can be used to determine the towed mass value which is equal to the mass of the trailer. The acceleration measurement along the y-axis Y can be used to determine the trailer sway value which quantizes tow vehicle and trailer sway. The acceleration measurement along the z-axis Z can be used to determine the suspension oscillation value which quantizes suspension oscillations of tow vehicle and trailer. 
     The top surface  42  of the instrument spacer  34  may also define a recess  68  receiving the data acquisition system  54  and the accelerometer  66 . A recess cover  70  may be disposed over the recess  68  to cover the data acquisition system  54  and the accelerometer  66  and protect those electrical components from the environment. The recess cover  70  attaches to the top surface  42  of the instrument spacer  34 . Attachment of the recess cover  70  to the top surface  42  of the instrument spacer  34  may be accomplished in many ways including but not limited to the use of screws, bolts, nails, rivets, clips, clamps, adhesives, welds, and sliding tracks. 
     The pair of sides  40  of the instrument spacer  34  may extend downwardly from the bottom surface  44  of the instrument spacer  34  to define a pair of ridges  72 . The pair of ridges  70  project from the bottom surface  44  of the instrument spacer  34  and engage the hitch support  22 . The pair of ridges  72  in conjunction with the hitch  24  and nut  32  secure the instrument spacer  34  to the hitch support  22 . More specifically, the instrument spacer  34  is sandwiched between the hitch base  26  and the hitch support  22  as the nut  32  is tightened about the lug  30  of the hitch  24  to prevent axial movement along the central bore axis A. The pair of ridges  72  engage the hitch support  22  to prevent rotation of the instrument spacer  34  about the central bore axis A relative to the hitch support  22 . 
     The subject invention also provides a method for monitoring a trailer hitch assembly  20 . The trailer hitch assembly  20  includes a hitch support  22 . The trailer hitch assembly  20  also has a hitch  24  including a hitch base  26  having a hitch base radius R H  and a lug  30  extending from the hitch base  26 . The trailer hitch assembly  20  further includes an instrument spacer  34  disposed between the hitch base  26  and the hitch support  22 . The instrument spacer  34  defines a cylindrical bore  46  receiving the lug  30  of the hitch  24 . The cylindrical bore  46  extends along a central bore axis A. The cylindrical bore  46  has a bore face  48  and a bore radius R B  that is less than the hitch base radius R H . The trailer hitch assembly  20  further includes at least one strain gauge  50  disposed on the instrument spacer  34  generating a resistance change and a user information display  64 . The method comprises the steps of positioning the at least one strain gauge  50  on the instrument spacer  34  at a radial distance D from the central bore axis A that is less than or equal to the hitch base radius R H  and greater than or equal to the bore radius R B . The method proceeds by measuring the resistance change of the at least one strain gauge  50  using a Wheatstone bridge circuit  56 , calculating a resultant force value in response to measuring the resistance change of the least one strain gauge  50 , calculating a torque value in response to measuring the resistance change of the least one strain gauge  50 , and displaying at least one of the resultant force value and the torque value on the user information display  64 . The method may also include the step of positioning the at least one strain gauge  50  on the bore face  48 . 
     The method may also including monitoring a trailer hitch assembly  20  also including an accelerometer  66  providing acceleration measurement along an x-axis X, a y-axis Y, and a z-axis Z. The method may further comprise the steps of calculating a towed mass value in response to the acceleration measurement along the x-axis X, calculating a trailer sway value in response to the acceleration measurement along the y-axis Y, and calculating a suspension oscillation value in response to the acceleration measurement along the z-axis Z. The towed mass value is equal to the mass of the trailer. The trailer sway value quantizes tow vehicle and trailer sway. The suspension oscillation value quantizes suspension oscillations of tow vehicle and trailer. 
     Obviously, many modifications and variations of the present invention are possible in light of the above teachings and may be practiced otherwise than as specifically described while within the scope of the appended claims. These antecedent recitations should be interpreted to cover any combination in which the inventive novelty exercises its utility. The use of the word “said” in the apparatus claims refers to an antecedent that is a positive recitation meant to be included in the coverage of the claims whereas the word “the” precedes a word not meant to be included in the coverage of the claims.