Abstract:
A stability sensing and load monitoring system for wheeled vehicles, in particular for the construction and agricultural industries, is disclosed. The system is based on strain sensors mounted on each wheel such that the measured strain represents the load on this wheel. A power source and a local wheel controller are located near the strain sensors. The data from the strain sensors is processed by the local wheel controller and then wirelessly transmitted to a single central unit, located in the cabin. The central controller communicates with all four local wheel controllers, collects the data, and then processes it to calculate the total load on the vehicle, its center of gravity, and the stability status.

Description:
BACKGROUND OF THE INVENTION  
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to the area of stability sensing and on board load monitoring for wheeled vehicles in general and in particular for trucks, off road vehicles, construction and agricultural vehicles, and mobile cranes. 
         [0003]    2. Description of Related Art 
         [0004]    Cranes and vehicles with hydraulic booms must sense and control their stability. A common stability sensing technique is to measure the extension of the boom, its orientation and elevation angles, and in addition to estimate or sense the load on the boom. Having collected these data a destabilizing moment can be calculated and compared to the allowed limits. 
         [0005]    Being indirect and relying on approximation, this approach is not very accurate. It is also relatively expensive as several costly sensors are necessary. 
         [0006]    A different approach is common in certain types of construction machines, like telescopic handlers etc, in which the rear axle is instrumented, normally with Extensometers, to sense the axle bending due to the forces which are transferred to the wheels. The controller of these machines watches for reduction of the bending of the axle, which in turn indicates less load on the rear wheels, more forward tipping moment, and reduction in forward stability. 
         [0007]    While relatively inexpensive, these systems suffer inaccuracies, are sensitivity to steering actions, and are not capable of sensing lateral or backward stability. 
       SUMMARY OF THE INVENTION  
       [0008]    The present invention provides important information to operators of certain vehicles: stability warning, total load on the vehicle, and center of gravity. The stability information is based on a simple observation: objects which are supported on four points are about to lose stability when any two adjacent supports cease to transfer load to the ground. Although not a novel principle, its implementation is novel and is therefore part of the present invention. 
         [0009]    Several types of mobile machines, serving the construction industry, agriculture and so on are not inherently stable and carry the risk of losing stability, toppling over and risking life and property. Other vehicles like trucks, although more stable, can be handled carelessly in driving and lose their stability as well. It has been therefore the goal of manufacturers of such machines and vehicles to use stability sensing and activate warning signals or stop or reverse machine functions when approaching instability is sensed. Total load monitoring is sought after to avoid maximum axle load regulations as well as to ensure structural safety. 
         [0010]    Since the points of contact with the ground in all wheeled vehicles are the wheels, it is best to sense the load being transferred by the wheels to the ground and to watch for loss of said load in any two adjacent wheels. Furthermore, any load transferred by the wheel to the ground is equal to the load placed on the same wheel by the axle to which it is connected; and, since a load on any wheel creates stresses and strains inside the rim structure, with the word rim relating to the metal structure between the axle and the tire, these stresses and strains being roughly proportional to the magnitude of the load, the present invention uses stress or strain sensors in all the vehicle wheel rims to measure said loads. In an alternative design the wheel loads are sensed by detecting a distortion of the rim under load which in turn is expressed by a change in the position of the center of each wheel relative to the outer circumference of the same rim. 
         [0011]    Information from the individual wheel sensors is wirelessly transmitted to a central controller (CC), usually installed in the cabin of the vehicle. Electrical power is supplied to the wheel sensors by batteries or by photovoltaic panels. 
         [0012]    A number of devices can be used as strain sensors: proximity sensors, extensometers, strain gage bridges, strain gage half bridges, or special load cells known by the name “Gozinta”. Installed or bonded in selected locations on the rims of the wheels, these sensing elements in each wheel are wired to a small local wheel controller (LWC). The latter performs several functions: it controls the voltage supply and distributes it to each strain sensor in the wheel; it collects the output reading from each strain sensor, filters, amplifies and digitizes it, and then, using certain algorithms, processes all the individual strain sensor readings into one single number representing the load on the said wheel; and, finally, it wirelessly transmits the said resulting load value to the CC. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0013]    Referring to the drawings for the purpose of illustration only and not limitation, there are the following depictions: 
           [0014]      FIG. 1  is a schematic cross section through a rim of a vehicle built according to the preferred embodiment. 
           [0015]      FIG. 2  is a front view of the same rim faced from the extension of its center line. 
           [0016]      FIG. 3  is a schematic representation of the entire system according to the present invention. 
           [0017]      FIG. 4  is a cross section through a variation on the preferred embodiment, necessary with certain designs of the rims. 
           [0018]      FIG. 5  depicts a front view of a different embodiment of the present invention, utilizing strain gages as sensors. 
           [0019]      FIG. 6  is a cross section through the same embodiment as in  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    Although specific embodiments of the present invention will now be described with reference to the drawings, it should be understood that such embodiments are by way of example only and merely serve to illustrate but a small number of the many possible specific embodiments which can represent applications of the principles of the present invention. Various changes and modifications obvious to one skilled in the art to which the present invention pertains are deemed to be within the spirit, scope, and contemplation of the present invention as further defined in the appended claims. 
         [0021]    Referring to  FIGS. 1 and 2 , shown is a rim of a vehicle with  FIG. 1  being a cross section and  FIG. 2  a front view. The rim consists mainly of a round circumference part  26  on which a tire is installed, and a vertical wall  36  connected to  26  in the circumference and to a central area  34  which in turn is attached to axle  38  with a number of bolts passing through holes  37 . Relief cuts  32  may or may not exist, depending on the practices in the rim manufacturing industry. The presence of cuts  32  or the absence thereof changes the stresses and strains in the rim and has to be taken in account for positioning the stress or strain sensors, but the present invention is valid for both situations. 
         [0022]    For the purposes of the present invention, the rim according to the preferred embodiment consists of:
       A folded channel  29 , built into wall  36  either by bending the sheet metal of wall  36 , as is shown in  FIG. 1 , or by welding a separately prepared folded part onto wall  36 .   Proximity sensors or extensometers  30  installed inside folded channel  29 .   Electric power source  35  installed inside folded channel  29 .   Local wheel controller  41 , installed inside folded channel  29 .   Wiring  40 , also installed inside folded channel  29  and connecting sensors  30 , power source  35 , and local wheel controller  41 .   A rugged protective cover  32 .       
 
         [0029]    Folded channel  29  extends through the entire  360  degrees of the rim, whether cuts  32  exist or not. In the case of existence of windows  32 , folded channel  29  continues through the windows leaving open area in one or both sides of itself depending on the layout of the said windows. Proximity sensors or extensometers  30  are installed on the mainly horizontal segment  39  of folded channel  29 . At least two sensors are required, preferably located  90  degrees from each other, but more sensors are preferred for better output signal and higher accuracy. When using three or more sensors they are evenly separated. There exist a small distance d between each sensor and the opposing horizontal segment  31  of folded channel  29 . Distance d changes under load W, and these changes are picked up by sensors  30  with the output of each sensor representing the local bending and stresses and strains. Since the wheel normally rotates when the vehicle is moving, and since the direction of loading is fixed with the reaction R always directed from the contact point of the tire on the ground upward to the rim center, it follows that distance d varies according to the momentary angular orientation relative to the rim&#39;s contact point on the ground. It is the assumption of the present invention that the combined reading of all sensors, when processed mathematically according to an appropriate algorithm, results in a number which is proportional to load W regardless of the current orientation of the rim/wheel. It is therefore the claim of the present invention that the combined reading of all sensors in an individual rim represents the load on same rim/wheel whether or not the vehicle is moving. However, in case the vehicle is moving, special processing of the readings can be utilized for better accuracy as follows: the reading from each sensor is highest when, due to the rotation of the rim, said specific sensor arrives closest to the ground contact point. Sequentially collecting the peak readings from all the sensors thus provides more data and enables averaging for all sensors for better accuracy. 
         [0030]    Folded channel  29  serves two purposes:
       A. Because the fold leads to bending stresses in itself as opposed to tension/compression taking place in a straight vertical wall  36 , it provides an area with increased deflection when the rim is acted on by force W. Such increased deflection facilitates higher and better output from the sensors.   B. It provides a protective housing for sensors  30 , wiring  40 , local wheel controller  41 , and power source  35 . When covered on its open side by cover  32 , there results a ruggedly protected space for all the elements in the system.       
 
         [0033]    Local Wheel Controller (LWC)  41  is electrically connected to all the sensors as well as to the electric power source  35 . It processes the outputs from the sensors and combines it into a single output signal which is proportional to the load W on the rim/wheel. Said output signal, which can be analog or digital, is then wirelessly transmitted to a the Central Controller in the cabin (CC, part  18  in  FIG. 3 ), where it is displayed, used for alarms, warnings and control of vehicle functions in case instability or maximum load are approached. For the wireless transmission an antenna is connected to the LWC (not shown) such that it lies in the external side of folded channel  29  or cover  32 , such antenna possibly consisting of an insulated wire bonded to the external metal surface of folded channel  29  or cover  32 . Since the antenna is on the external side of the mentioned parts  29  and  32 , the connecting wire to the LWC has to penetrate the metal through a small hole (again not shown). Said hole will be sealed around the wire; alternatively, a “glass to metal” device can be used for the same purpose. 
         [0034]    The electric power supply in the preferred embodiment is a set of batteries located inside folded channel  29 . To save on power consumption, LWC  41  will use techniques like sleep mode and low duty cycle for operating the sensors. 
         [0035]    Cover  32  is made of metal formed with a fold of its own. That way, even when made of heavy and rugged steel to effectively protect the content of folded channel  29 , it still presents low resistance to the bending of folded channel  29 , thus retaining high outputs. Cover  32  will be held in place against vertical wall  36  by bolts, in which case it can be removed for maintenance or for battery replacement. Alternatively it can be welded in place leaving a short portion near the battery to be held by screws, this portion therefore serving as access door for replacement of batteries. A gasket seal between cover  32  and wall  36  will keep the system protected from the environment. 
         [0036]    In the above mentioned embodiment, sensors  30  are called out as proximity sensors or extensometers. Both types, when properly selected, have the ability to detect very small distance shifts. Proximity sensors have an advantage in that they need to be installed on one side only with the other side serving as a target whose distance is sensed. Extensometers, on the other end, need to be clamped to both sides. 
         [0037]      FIG. 3  was already mentioned briefly. It schematically depicts the entire stability and load sensing system according to the present invention. Items  14 , 15 , 16 , and  17  are all the four wheels of a vehicle. Item  7  represents the LWC,  41  in  FIG. 2 , containing the wireless transmitter/receiver and its antenna.  18  is the central controller (CC) which in turn is located inside the cabin of the vehicle and which consists of receiving/transmitting circuits, software, power supplies fed by the vehicle power source, display means, operator input means, and control outputs like relays. CC  18  receives and transmits signals from and to each of the wheels, processes the information and arrives at several resulting numbers which represent the total load on the vehicle, load on each of the four wheels, center of gravity of the vehicle, and stability status. These results may then be displayed, warnings sound, and control output sent to activate or deactivate vehicle functions. 
         [0038]      FIG. 4  depicts a cross section of a rim  55  built integrally with a “channel”  45 . Such construction of the rim enables a the use of a simpler variation of the preferred embodiment. In this embodiment, integral channel  45  is used for the same purposes as the folded channel  29  in  FIGS. 1 and 2 , namely to provide bending deflection as well as to hold and protect the various system elements. Item  44  represents the proximity sensors or the extensometers which detect changes in distance d from the sensor to surface  56 . As in the preferred embodiment above, the minimum number of sensors is two but three or more will provide better accuracy. Cover  43  seals and protects the parts in channel  45 . 
         [0039]      FIGS. 5 and 6  depict yet another embodiment of the present invention, based on strain gages as load sensors.  FIG. 5  is a front view of a rim  57  and  FIG. 6  is a cross section through it. Rim  57  may or may not have relief cuts  47 , depending on the design of the rim itself. Strain gage bridges or half bridges  46  are bonded on vertical wall  58  in several locations, evenly distributed around the wheel. At least two bridges are needed but three or more will provide better accuracy. Wires  53  connect the bridges to LWC  51  and to electric power source  52 . The rim is connected to its axle through area  49  with bolts passing through holes  50 . A cover  54  is attached to wall  58  with bolts and serves to ruggedly protect the system components. Cover  54  is sealed against wall  58  with a gasket (not shown). When a load is applied on rim  57  in a manner similar to the one shown in  FIG. 1 , stresses and strains appear within wall  58  which are then detected by strain gage bridges  46 . Mathematically combining all individual bridge readings can result in a number representing that said load. 
         [0040]    Yet another embodiment is not shown but is based on replacing strain gage bridges with devices widely known as “Gozinta”. Each Gozinta is a load cell base on strain gages and has a general shape of a small and short cylinder sealed at both ends. Gozinta&#39;s are designed to be pressed inside holes in stressed members thus saving the need for bonding operation in the field. Once in place, the Gozinta senses the strains in the substrate in which it is pressed and in that way serves as a strain sensor. 
         [0041]    Still another embodiment, again not shown, is based on replacing strain gage bridges with Extensometers.