Abstract:
A vehicle weight determination apparatus is disclosed which includes a receiver; a persistent memory storing a plurality of sensor identifiers, a like plurality of axle identifiers and a like plurality of correlation information, such that a given sensor identifier is associated with a given axle identifier and given correlation information. The apparatus also includes a controller for: receiving from the receiver a message comprising a sensor identifier and an air pressure indication, utilitising the sensor identifier to obtain an axle identifier and correlation information, and utilising the correlation information and the pressure indicator to obtain a weight measure associated with the axle identifier. The apparatus may include a display for displaying the weight measure and the axle identifier.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application claims priority from U.S. provisional application No. 60/763,893, filed Feb. 1, 2006, the contents of which are hereby incorporated herein by reference. 

   BACKGROUND 
   This invention relates to vehicle weighing. 
   It may be desirable to know the weight of a commercial vehicle for a number of reasons. Firstly, the amount charged for transporting cargo by vehicle is normally based upon distance to destination and on the weight of the cargo. Cargo weight may be determined by subtracting the loaded weight of the vehicle from its empty weight. Secondly, it is inefficient to drive a partially loaded vehicle. To avoid this, a vehicle could be loaded with a variety of different loads, however, in such instance the vehicle can be weighed to ensure the loads do not exceed the maximum capacity of the vehicle. Further, public authorities have an interest in ensuring certain weight restrictions are adhered to on public highways in order to protect the public infrastructure. And fines may be levied on vehicles which exceed specific weight limitations. 
   While weigh scales can be used to obtain the axle weight, and total weight, of vehicles, scales may not be conveniently available when needed. For this reason, a number of on-board weighing systems have been developed. 
   Nevertheless, there remains a need for an improved on-board vehicle weighing approach. 
   SUMMARY OF INVENTION 
   According to one aspect of the invention there is provided a method for determining a vehicle weight comprising: receiving a message comprising a sensor identifier and a weight related parameter indication; utilising the sensor identifier to obtain correlation information; obtaining a weight measure based on the weight related parameter indication and the correlation information. 
   According to another aspect of the invention there is provided a vehicle weight determination apparatus, comprising: a receiver; a persistent memory storing a plurality of sensor identifiers, a like plurality of axle identifiers and a like plurality of correlation information, such that a given sensor identifier is associated with a given axle identifier and given correlation information; a controller for: receiving from the receiver a message comprising a sensor identifier and an air pressure indication, utilitising the sensor identifier to obtain an axle identifier and correlation information, utilising the correlation information and the pressure indicator to obtain a weight measure associated with the axle identifier. 
   According to another aspect of the invention there is provided a vehicle weight determination apparatus, comprising: a pressure transducer; a transmitter; a persistent memory for storing a sensor identifier; a controller for: receiving a pressure indication from the pressure transducer and a temperature indication from the temperature transducer; retrieving the sensor identifier; constructing a message comprising the sensor identifier, the pressure indication, and the temperature indication; controlling the transmitter to send the message. 
   According to another aspect of the invention there is provided a method for determining a vehicle weight comprising: generating a message comprising a sensor identifier and a weight related parameter indication; broadcasting the message to a unit comprising a receiver; the receiver receiving the message; the unit utilising the sensor identifier to obtain correlation information; the unit obtaining a weight measure based on the weight related parameter indication and the correlation information; displaying the weight measure on a display associated with the unit. 
   According to another aspect of the invention there is provided a system for determining a vehicle weight comprising a sensor and a unit: the sensor operable to generate a message comprising a sensor identifier and a weight related parameter indication and broadcast the message to the unit; the unit comprising a receiver for receiving the message broadcast from the sensor and the unit operable to utilise the sensor identifier to obtain correlation information stored in a database; the unit operable to generate a weight measure based on the weight related parameter indication and the correlation information and operable to display the weight measure on a display associated with the unit. 
   According to another aspect of the invention there is provided a kit comprising: a sensor and a unit; the sensor comprising a housing and being operable to generate a message comprising a sensor identifier and an air pressure indication and broadcast the message to a unit; the hand held device comprising a receiver for receiving the message broadcast from the sensor and the unit operable to utilise the sensor identifier to obtain correlation information stored in a database; the unit operable to generate a weight measure based on the air pressure indication and the correlation information and operable to display the weight measure on a display in the unit; the kit further comprising a length of tubing and a connector, the connector adapted for being inserted into an air vehicle suspension line of a vehicle air suspension system, and the length of tubing adapted to connect an outlet of the connector to an inlet to the housing of the sensor. 
   According to another aspect of the invention there is provided a method of retrofitting a vehicle comprising an air suspension system, the air suspension system comprising at least one air spring associated with an axle or axle group, the air spring comprising an air line for supplying pressurized air to the air spring, the method comprising: attaching a sensor to the vehicle, the sensor comprising an inlet for receiving communication of pressurized air, the sensor operable to generate a message comprising a sensor identifier and an air pressure indication related to pressure of the pressurized air and broadcast the message to a unit; introducing a connector into the air line in the air suspension system to provide an outlet; connecting the outlet of the connector to the inlet of the sensor, so as to communicate pressurized air from the air line to the inlet of the sensor. 
   According to another aspect of the invention there is provided a sensor comprising a housing comprising an inlet for receiving communication of pressurized air, the sensor operable to generate a message comprising a sensor identifier, and an air pressure indication related to a pressure of the pressurized communicated to the inlet, and broadcast the message to a unit. 
   According to another aspect of the invention there is provided a method for determining a weight of a vehicle comprising: providing a plurality of sensors, each of the sensors associated with an axle or axle group of the vehicle; each sensor generating a message comprising a sensor identifier and a weight related parameter indication; broadcasting each message from each sensor to a unit. 
   According to another aspect of the invention there is provided a method for determining a weight of each of a plurality of vehicles comprising: providing at least one sensor for each vehicle of a plurality of vehicles; each sensor generating a message comprising a sensor identifier and a weight related parameter indication; broadcasting each message from each sensor to a unit. 
   According to another aspect of the invention there is provided a kit comprising: a sensor comprising a housing and the sensor being operable to generate a message comprising a sensor identifier and an air pressure indication and broadcast the message to a unit; a length of tubing; a connector adapted for being inserted into an air vehicle suspension line of a vehicle air suspension system, and the length of tubing adapted to connect an outlet of the connector to an inlet to the housing of the sensor. 
   According to another aspect of the invention there is provided a method for determining vehicle weight information comprising: (a) broadcasting a message comprising a sensor identifier and a weight related parameter indication; (b) utilizing the sensor identifier to obtain correlation information; (c) obtaining a weight measure based on the weight related parameter indication and the correlation information. Steps (a)-(c) may be repeated at a periodic interval. 
   According to another aspect of the invention there is provided a method for determining a weight of a vehicle comprising: providing a sensors associated with an axle or axle group of the vehicle; the sensor generating a message comprising a sensor identifier and a weight related parameter indication; broadcasting each message from each sensor to a unit at a periodic interval. 
   The periodic interval may be variable and may be varied by an external input. The methods may also include measuring the change in the weight related parameter over an interval of time; monitoring said measured change to determine when said measured change exceeds a threshold level; and when said measured change exceeds said threshold level, adjusting the value of said periodic interval. The value may be adjusted to shorten the length of said periodic interval. The interval of time may correspond to said periodic interval. The weight related parameter indication may be an air pressure indication. Other features and advantages will become apparent from the following description in conjunction with the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the figures which illustrate an example embodiment of the invention, 
       FIG. 1A  is a schematic side view of a vehicle suitable for use with this invention, 
       FIG. 1B  is a schematic rear view of the vehicle of  FIG. 1A  showing a portion of a weight sensing system according to an embodiment of this invention, 
       FIG. 2  is a schematic view of the sensor of  FIG. 1 , 
       FIG. 2A  is a perspective view of the sensor unit; 
       FIG. 3  is a schematic view of a central unit, 
       FIG. 3A  is a perspective view of the central unit, 
       FIG. 4  is a view of a table stored in memory of the unit of  FIG. 3 , 
       FIG. 5  is a screen shot from the display of the unit of  FIG. 3 , and 
       FIG. 6  is another screen shot from a display of the unit of  FIG. 3 . 
   

   DETAILED DESCRIPTION 
   Turning to  FIGS. 1A and 1B , a vehicle  10  may have a truck  11  pulling a trailer  13 . The trailer may have a body  12  resting on long sills or rails  14 . As is typical with a large number of commercial cargo carrying vehicles, the suspensions are air springs. Thus, for trailer  13 , the long sills  14  of the body  12  may be coupled to each axle  16  of the trailer through air springs  20 . Each axle may terminate in wheels  22 . The air pressure for the air springs may be provided through an air pressure line  24  which may be supplied by a compressor (not shown) driven by the motor of the truck  11  pulling the trailer  13 . A valve  26  may be incorporated into the air line supplying the air springs  20  for an axle  16  so that the air pressure supplied to the air springs may be regulated based on the weight of the load in the trailer so that the air springs do not allow the long sills to bottom out (i.e., impact the axles) as the trailer travels. 
   A sensor  30  may be connected to air pressure line  24  between the valve  26  and air springs  20  through T-connector  32  and line  25 . In consequence, the sensor  30  is in fluid communication with the air inside air springs. The sensor  30  may be attached to the frame of the trailer, such as to one of the long sills  14 . While not shown in the drawings, the sensor may be mounted to the outside surface of the sill, which as will be explained in further detail hereafter, may provide for a greater broadcasting range for its transmitter. 
   Turning to  FIG. 2 , sensor  30  may comprise a transmitter  32 , pressure transducer  34 , temperature transducer  36  and memory  38  in communication with a controller  40 . The pressure transducer  34  may be any conventional pressure transducer, such as a piezoresistive pressure sensor. For example, pressure transducer  36  may be the model 1451 sensor made by KS Sensors. The temperature transducer may also be any conventional temperature transducer. For example the temperature transducer may be a thermistor. The controller  40  may be, for example, a programmed processor or a field programmable field array. Memory  38  may be a persistent memory, such as a flash memory. Memory  38  stores an identifier  42  of sensor  30 , such as a unique sensor serial number. The sensor may be battery powered. For example, the sensor may be adapted to be powered by two “AA” batteries. 
   Controller  40  may be configured to periodically read a pressure reading from pressure transducer  34  and a temperature reading from temperature sensor  36  and compensate the pressure reading based on the temperature reading. The sensor may then retrieve the sensor identifier  42  and construct a message with the sensor identifier and compensated pressure reading. The message may then be sent by the controller to transmitter  32  which wirelessly broadcasts the message over antenna  46 . The transmitter may be configured to employ any suitable encoding and modulation scheme in transmitting the message. 
   While temperature compensation may be effected in any known manner, one suitable approach is to amplify the output from pressure transducer  34  by an amplifier (not shown) whose gain and voltage offset values have been appropriately selected. More specifically, at the factory, the output voltage from the pressure transducer may be measured at three temperatures: say −20° C., 20° C. and 60° C. Suitable offset voltage and gain correction values at these temperatures for the amplifier may then be determined and stored in the memory  38  of sensor  30 . On the other hand, if a temperature reading from temperature transducer  36  of sensor  30  is higher than the middle one of the three stored temperatures, the stored gain and offset values at the higher two temperatures are used to linearly interpolate a gain and offset for the temperature read. The linearly interpolated gain and offset values are then applied to the amplifier so that the output of the amplifier is a temperature compensated pressure indication. Thereafter, if a temperature reading from temperature transducer  36  of sensor  30  is lower than the middle one of the three stored temperatures, the stored gain and offset values at the lower two temperatures are used to linearly interpolate a gain and offset for the temperature read. The linearly interpolated gain and offset values are then applied to the amplifier so that the output of the amplifier is a temperature compensated pressure indication. 
   A sensor  30  may be associated with each of the other axles of the trailer  13  and with each of the axles of the truck  11 . 
   As shown in  FIG. 2A , sensor  30  may have a housing  31  which houses the aforementioned components of the sensor, that is, transmitter  32 , pressure transducer  34 , temperature transducer  36 , memory  38 , controller  40  and the batteries which power the active components. Housing  31  may be a waterproof and weatherproof sealed housing  31  made from any suitable material, such as ABS plastic material or anodized aluminum. 
   Housing  31  may assist in resisting the effects of shocks that might result from impacts such as from rocks and the like when the vehicle is moving on a roadway. 
   Housing  31  may have a label  33 , such as a bar code label or an RFID label, which incorporates the sensor identifier (which, as noted, may be a unique serial number associated with the sensor). 
   Housing  31  may have a fitting  35  which may be connected to tubing  25  ( FIG. 1B ) to interconnect the sensor  30  to the vehicle air suspension system through T-connector  32  ( FIG. 1B ), as is further described hereinafter. Fitting  35  provides the inlet to the sensor  30  to put pressure transducer  34  in communication with the air springs so the air pressure in air springs can be measured. 
   With reference to  FIG. 3 , a central unit  50  comprises a receiver  52 , memory  54 , user interface  56 , and display  58  all of which are communicatively coupled to a controller  60 . The controller may be, for example, a programmed processor. Memory  54  may be a persistent memory, such as a flash memory. The memory may store a database  62 . The unit may be battery powered. As shown in  FIG. 3A , the various components of central unit  50  may be housed in a case  51  that may be made from a suitable material, such as plastic. The central unit  50  may be sized as, and used as, a handheld device. Alternatively, the unit  50  may be attached within the cab of truck  11  ( FIG. 1A ). 
   Turning to  FIG. 4 , database  62  may store information which represents a table  70  with a column  72  for sensor identifiers, a column  74  for axle identifiers, and a column  76  for correlation information. The correlation information column may be divided into a sub-column  78  for empty weight in pounds, a sub-column  80  for pressure in pounds per square inch (PSI) and a sub-column  82  for slope in pounds per PSI. Thus, any row of table  70 , such as row  84 , will represent a sensor identifier and an associated axle identifier and correlation information. 
   Returning to  FIG. 3 , when receiver  52  receives a wireless message over its antenna  88 , it may demodulate and decode the message as necessary and pass it to controller  60 . The transmitter  32  may have a range of in the order of up to 500 to 1,000 feet. The controller  60  may parse the message for a sensor identifier, a pressure indication, which may be in PSI, and a temperature indication. The controller may utilise the sensor identifier as a key into table  70 . Thus, the controller may retrieve the row of information associated with the sensor identifier in the incoming message and thereby obtain an axle identifier and correlation information associated with the sensor identifier. The controller  60  may be configured to utilise the correlation information to convert the pressure indication to a weight measure associated with the axle identifier. The controller  60  may then display this information, along with the pressure indication, on its display  58 . 
   An exemplary screen shot on display  58  is illustrated in  FIG. 5 . Turning to  FIG. 5 , screen shot  90  may have a trailer depiction  92  depicting trailer  13  ( FIG. 1A ) and a truck depiction  94  depicting the truck  11  ( FIG. 1A ) pulling the trailer. Each axle or axle group of the vehicle may also be depicted, here axle depiction  86  and axle group depictions  96  and  106 . The screen shot may display a bar  108  to indicate a particular axle group and a weight indication  110  of the weight associated with the axle group indicated by bar  108 . The weight displayed may be that determined by controller  60  ( FIG. 3 ) as aforedescribed. The screen shot may also show a pressure indication at  112  and a brace  115  for each other axle or axle group for which an associated pressure and weight may be displayed. The screen shot may also have a time and/or date indication  114  if a time clock is associated with unit  50  and outputs to controller  60 . 
   Each sensor  30  may broadcast an updated message once per minute and the controller  60  of unit  50  may display the received pressure indication and the determined axle group weight based on messages received from sensors in serial fashion. Alternatively, unit  50  may display an axle group weight based on a selection made via user interface  56 . 
   Once the controller  60  has received an axle (or axle group) weight from the sensor for each axle (or axle group) of vehicle  10 , it may determine a total vehicle weight and also display this. Screen shot  90  shows this at total weight depiction  116 . 
   Unit  50  may have two modes: a locked mode wherein the unit operates as described hereinabove, and a configuration mode. In the configuration mode, through user interface  56 , a user may select a vehicle type and associate a sensor identifier with each axle and axle group of the selected vehicle type. For example, unit  50  may store the vehicle depictions illustrated in  FIG. 6  for display on display  58 , each of which depictions shows a different vehicle type. Each vehicle depiction shows a specified number of sensor locations, with each sensor associated with a particular wheel axle or wheel axle group. Once the user has selected a vehicle type and entered a sensor identifier (obtained from label  33  of the sensor) associated with each axle or axle group of the selected vehicle type, the user may also associate (i) an empty weight and an empty pressure and (ii) a full weight and a full pressure with each sensor. This can be done by using a conventional weight scale to calibrate each sensor. More specifically, the vehicle can be driven to a conventional weight scale with no load in the trailer. The empty weight may then be recorded for each axle or axle group of the vehicle and this information entered into unit  50 . The process may be repeated at the weight scale when the vehicle is fully loaded, and the loaded weight recorded for each axle or axle group and then entered into unit  50 . With this information, the controller  60  of unit  50  may determine the correlation information to associate with each sensor  30  and store into table  70 , thereby calibrating each sensor. 
   More specifically, with the axle/axle group empty weight and pressure, and full weight and pressure, assuming a linear relationship between weight and pressure, the controller  60  can calculate a slope of the line relating pressure to weight and store this slope as part of the correlation information. With the empty weight and associated pressure, and the slope, the controller  60  can thereafter calculate the weight at any pressure. Greater accuracy would be possible if the effort were expended to determine additional pressure weight correlations for different partial loadings of the vehicle. With these additional correlations, the controller could model a non-linear relationship between pressure and weight as part of the correlation information. However, in many instances the increased accuracy is not sufficient to warrant the effort. 
   Each sensor  30  only needs to be calibrated once with unit  50  as the correlation information may be persistently stored for repeated use in measuring loads. 
   With a sufficiently large memory  54  in unit  50 , database table  70  could hold data for sensors from a plurality of trailers. Thus, if a truck  11  were used with two or more different trailers, a unit  50  could be used with the truck when pulling any of these trailers after sensor data for each of the sensors of the various trailers had been stored to table  70 . 
   The described system may be supplied as a kit and retrofit to a vehicle. The kit may include a central unit  50  and a set of sensors, each supplied with a T-connector and a length of tubing. The retrofit may proceed as follows. Firstly, a sensor  30  may be attached to the vehicle at each axle and axle group. The air line may be cut to introduce a T-connector  32  between the valve  26  and the air springs  20  of the axle/axle group and an air line  25  may be run from the free fitting of the T-connector to the sensor. The sensor identifier and associated axle/axle group for each sensor may be noted and input to unit  50  as aforedescribed. The vehicle may then be weighed empty and full so that axle group weight and associated pressure parameters may be input to unit  50  as aforedescribed. 
   The sensor can readily be operationally installed on the vehicle in a relatively short period of time, such as for example about 10-30 minutes. As it is not necessary to splice or connect to the vehicle&#39;s electrical system, only the air suspension system, many drivers/driver-operators are qualified to perform the installation themselves. Therefore, in many situations a visit to a fully qualified vehicle maintenance technician is not required. 
   In normal operation, the sensors may send the messages at a fixed periodic interval of time. Optionally, if each sensor  30  and unit  50  are provided with transceivers (rather than a transmitter and receiver, respectively) through user interface  56 , unit  50  may be set to prompt sensors  30  to alter the value of the periodic interval and may send pressure indication messages more frequently, say once every three seconds. This alteration in the periodic interval for sending messages may continue either for a predetermined period of time (such as for example about 15 minutes), or until it is again altered through the user interface. This allows near real time monitoring of the weight of the trailer during loading so as to guard against overloading. Alternatively, each sensor  30  may be configured such that if the rate of pressure change exceeds a threshold rate, the sensor automatically adjusts the periodic interval and may then send pressure indication messages more frequently. This avoids the need to configure unit  50  with a transceiver. Further, this feature may alert a user to a situation wherein a load is being lost. The altering of the periodic interval can then continue for a predetermined period of time (such as for example again about 15 minutes) or until it is again altered through the user interface. The alerting function is enhanced if unit  50  responds to receiving messages from a sensor at the higher rate by generating an alarm signal. 
   If unit  50  is provided with a transceiver, unit  50  could also be used to otherwise configure the sensors (e.g., poke new temperature compensation values into sensor memory). 
   While the vehicle to which the weight sensing system has been applied has been described as a truck pulling a trailer, obviously the system may be applied to other vehicle types, such as a tractor pulling a trailer, or a one-piece vehicle, such as a dumpster or van. 
   Optionally, a sensor  30  may be configured to generate a message which is related to another weight related parameter, rather than pressure in the air suspension system. For example, the displacement in a mechanical suspension, such as a leaf spring, coil spring or other mechanical suspension, can be measured and broadcast by sensor  30  to unit  50 . In this instance, unit  50  will have a weight/displacement correlation database table constructed in a manner similar to the database table  70  described above. 
   While unit  50  has been described as associated with a truck  11 , it would be possible to associate unit  50  with a central station, such as a central station for a vehicle fleet. In this instance, unit  50  may be provided with an extended memory. The memory of unit  50  could then store a row in its database table  70  for each sensor of each truck and trailer in the fleet. The unit  50  could then be used centrally to monitor vehicle weights. Indeed, if database  70  stored information for each sensor of each vehicle which was expected at a weigh station, unit  50  could be used to replace or supplement a conventional weigh station. Indeed, vehicles fitted with sensors  30  might avoid having to go through a conventional weigh scale facility instead passing through an area where a unit  50  can quickly retrieve the information broadcast from sensors  30  on vehicles so equipped. 
   Where it is expected that a unit  50  will store data from sensors on more than one trailer, it may be necessary for the unit  50  to also store a trailer identifier in association with each sensor in database table  70 . This trailer identifier may be entered by a user when the unit  50  is in its configuration mode. The user may then use the user interface  54  to select the identifier of the trailer currently part of the vehicle. If this is done, then unit  50  will ignore wireless signals that may be received from any sensors not associated with the selected trailer, even if data for those sensors is stored in database table  70 . 
   Optionally, the sensors could also store an axle group type description and ride height setting. This would be advantageous for a fleet of similar trailers which differ only in these parameters. In this situation, an empty and full weight calibration would only need to be performed for the sensors of one of the set of similar trailers and the calibration data then loaded to each unit  50  used with any of these trailers. A unit  50  could then correlate pressure from a sensor with a weight based on the common calibration data and the sensor specific axle group type description and ride height setting information. 
   Optionally, rather than table  70  storing an empty weight and associated pressure along with a slope, table  70  could store an empty weight and associated pressure, and a full weight and associated pressure. In each instance, controller  60  may calculate a correlation factor on-the-fly from this correlation information and a received pressure indication. 
   Optionally, messages from the sensors can be encrypted. 
   Other modifications will be apparent to those skilled in the art and, therefore, the invention is defined in the claims.