Abstract:
An electromechanical apparatus suitable for mounting on a vehicle wheel power for generating telemetry relating to the wheel including tire temperature and pressure. The apparatus includes a pendulum mounted to rotate freely relative to the vehicle wheel which is positioned from the wheel hub. When the wheel is set to rotation, the pendulum freely hangs from the wheel hub under the influence of an off center counterweight having sufficient inertia to prevent rotation of the pendulum with the wheel. The pendulum is used to position one or more magnets to be used to excite field coils, which are mounted with respect to the wheel hub to rotate with the wheel. The magnets and rotating coils cooperate to energize a power utilization circuit also mounted with respect to the wheel hub to rotate therewith. The utilization circuit may include such sensors as desired, typically including though a tire pressure gauge and tire and wheel hub temperature gauges. The apparatus is readily extended to incorporate a fire pressurization pump, which may be a solenoid pump powered indirectly from the rotating coils, or by a magnetic button pump.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to vehicle and wheel assembly condition monitoring and, more particularly, to a hub mounted sensor assembly which is self energized. 
     2. Description of the Problem 
     Economical truck operation and the reduction of vehicle maintenance costs are greatly aided by keeping the vehicle in close conformance to a manufacturer&#39;s operational specifications. Of particular concern here are those specifications relating to the operating condition of the vehicle axle and tire/wheel assembly. Maintaining proper fire pressure contributes directly to optimum fuel economy and to long fire life. Low tire pressure results in tire sidewall flex which contributes to a heat buildup in the tire. Excessively high tire temperatures promote degradation of the polymers from which tires are constructed which in turn promotes excessive wear of the tire. An axle end temperature which varies above a threshold temperature may indicate the beginning of a wheel bearing problem. 
     Truck operators routinely check tire pressure during stops, however, the ability to monitor all of these variables, and possibly to adjust tire pressure, while the vehicle is in motion, would be advantageous. However, accessibility to points where these variables can be measured, while the vehicle is in motion, is less than optimal. Typical active sensors, such as air pressure gauges and thermometers, work best if they can be placed in close proximity to, if not direct contact with, the object to be measured. On a vehicle, this means placing air pressure sensors onto the rotating wheel. If the condition is to be monitored from the vehicle&#39;s cab, some communication device must transfer data from the sensor to a read out device in the cab. On contemporary vehicles, in which instrumentation is highly, if not completely, electronic, this usually means providing power to an electronic sender for the wheel mounted sensor and providing a transmission channel for the data back to the cab. 
     Wheel mounted electronic measurement and transmission system have been suggested which use batteries installed on the rotating wheels or in the vehicle tire to provide power to signal processing electronics and data transmission. Radio transmission can then be used to provide data transmission to the vehicle cab. Such a system obviously requires occasional checks on battery condition. 
     The prior art also provides for tire repressurization for moving vehicles. An example of such a system which can be mounted on the rotating wheel is U.S. Pat. No. 5,667,606 to Renier. The Renier device uses a pendulum which hangs freely from a rotating wheel hub. The pendulum is attached to a cam on which a cam follower, attached to a piston which rotates with the hub, rides. As the cam follower rides up on the cam it displaces the piston inwardly until the end of the cam is reached, whereupon the cam follower falls off of the cam and is displaced outwardly by a compression spring in order to begin the cycle again. The piston is the active component of a pump which provides pressurized air to a reservoir which feeds fires is under inflated. The system provides no data transmission to an electronic controller or monitoring arrangement. 
     A system which can provide data to a central controller can be integrated with other vehicle control arrangements, or, at a minimum, can be used to alert the driver of a vehicle of out of specification operation. In addition, an electronic system more readily provides monitoring of diverse conditions. Providing such a system on a rotatable wheel with a minimum of additional maintenance concerns remains desirable. 
     SUMMARY OF THE INVENTION 
     The invention provides an electromechanical apparatus suitable for mounting on a vehicle wheel which provides power for sensors and telemetry from sensors on a wheel, including tire temperature and pressure. The apparatus includes a pendulum mounted to rotate freely relative to the vehicle wheel positioned from the wheel hub. When the wheel is set to rotation, the pendulum freely hangs from the wheel hub under the influence of an off center counterweight having sufficient mass to prevent rotation of the pendulum with the wheel. The pendulum is used to position one or more magnets to be used to excite field coils, which are mounted with respect to the wheel hub to rotate with the wheel. The magnets and rotating coils cooperate to energize a power utilization circuit also mounted with respect to the wheel hub to rotate therewith. The utilization circuit may include such sensors as desired, typically including a tire pressure gauge and tire and wheel hub temperature gauges. Some embodiments include tire pressurization pumps, which may in turn take one of several forms including solenoid pumps powered indirectly from the rotating coils, or by magnetic button pumps. 
     Additional effects, features and advantages will be apparent in the written description that follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is an exploded perspective view of a wheel sensor assembly in accordance with a preferred embodiment of the invention. 
     FIG. 2 is a side view in partial cross section of the wheel sensor assembly. 
     FIG. 3 is an exploded view of the wheel sensor assembly. 
     FIGS. 4A-B are views of a magnetic element used in the wheel sensor assembly. 
     FIGS. 5A-B are detailed views of the magnetic element of FIGS. 4A-B. 
     FIG. 6 is a block diagram of a power utilization circuit employed in the wheel sensor assembly of the present invention. 
     FIG. 7 is a block diagram of a power conditioning circuit utilized in the wheel sensor assembly of the present invention. 
     FIGS. 8A-B are a schematic illustration of an air pump used in one embodiment of the present invention. 
     FIG. 9 is a schematic illustration of an air transfer circuit used to deliver pressurized air to tires mounted on a wheel. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings and in particular to FIG. 1, a wheel sensor assembly  10  is illustrated. Wheel sensor assembly  10  is positioned at the end of a wheel axle  12 , typically found on a medium or heavy duty truck, and may be used to provide data relating to the operating condition of the axle end and for tires (not shown) mounted on wheels (not shown) depending from the axle  12 . Wheel sensor assembly  10  is directed to placing low maintenance energization components, power regulating and signal gathering, conditioning and transmitting circuitry into rotation with the wheels to avoid any need for direct mechanical or electrical connections between the vehicle and the sensor components. 
     Wheel sensor assembly  10  is positioned on a backing plate  14 , which in turn is mounted on axle  12 . Mounting plate  14  is mounted for rotation on axle  12 . Backing plate  14  is generally disk shaped and provides points of attachment for a housing  26  of the wheel sensor assembly  10 . Housing  26  rotates with the adjacent wheel of the vehicle. A shaft  16  extends outwardly from backing plate  14  relative to axle  12 . Shaft  16  mates with a bearing  20  which is positioned in the center of the disk shaped magnetic plate  18 . Magnetic plate  18  is set to rotate freely on shaft  16 , but tends to keep a fixed rotational position relative to axle  12  under the influence of a relatively substantial inertial mass provide by an off center weight or pendant  22 , attached to a face of the plate facing backing plate  14 . A plurality of magnets  38  form the other major face of the disk shaped magnetic plate  14 . Magnets  38  are flattened, pie section shaped pieces which, when fitted together form a disk facing substantially covering the outer portion of one major surface of magnetic plate  18 . 
     Housing  26  is positioned on backing plate  14  to enclose magnetic plate  18  and a pair of field coils  24  wound on laminate substrate. Field coils  24  are mounted within housing  26  to rotate with the housing and the backing plate. Housing  26  further provides a attachment position for a printed circuit board  32 , and a cap or cover  34  enclosing the circuit board. An air pressure sensor  28  and air pressure inlet connection point  30  may also be positioned on the exterior shell of housing  26 . 
     Referring now FIGS. 2-3, backing plate  14  is mounted on one side of an axle end plate  13  facing away from an end to end axle  12 . Housing  26  is mounted along rim  84  in a circular recess  86  on the outward face of backing plate  14 , and encloses a volume in which shaft  16 , magnetic plate  18  and field coils  24  are enclosed. Wheel sensor assembly  10  is illustrated as assembled on backing plate  14 . Shaft  16  has a threaded male end  48  which is screwed into a cooperatively threaded receiving bore  49  in back support plate  14  to position the shaft, centered in the exposed major surface and extending perpendicularly from the surface. The opposite end of shaft  16  is a reduced diameter section  47  which mates with a shaft bore  96  defined by bearing  92  (shown in FIG.  5 A), which is centered in magnet mounting plate  40 . 
     One or more magnets  38  may be placed on an outward face  41  of magnet mounting plate  40 . A magnet  38  and field coil  24 , when rotated to bring it adjacent the magnet, should be spaced by gap set to minimize flux leakage without risk of contact between the coil and the magnet. A off center counterweight or pendant  22  is attached to the face of magnet support plate oppositely faced from the face  41 . Pendant  22  tends to bring magnetic plate  18  to a substantially fixed rotational position relative to axle  12  with the pendant below and vertically aligned by gravity with the axis of rotation of plate  18 . Field coil  24  is mounted to the interior face of wall  54  which defines the shell of housing  26 . Where the sensor assembly also provides tire inflation, a magnetic button pump  42  may also be mounted on the interior surface of wall  56 . Magnetic button pump  42  is described in greater detail below. A pair of wires  54  is connected between field coil  24  and a printed circuit board  32  which is housed within cover  34 . A breather valve  52  allows air to be admitted from exterior of housing  26  via a channel through wall  56  to the interior of housing  26 . Tire pressurization valves  50  are also connected by channels  51  running through the interior of housing  26  between pumps, such as pump  42  or solenoid pumps (shown below). 
     In the exploded view, it may be seen that axle shaft end  11  provides a foundation for mounting backing plate  14 . Backing plate  14  comprises two generally disk shaped elements, an larger base plate  13  adapted to provide an interface between the axle shaft end  11  and a mating disk  17  which provides attachment points for housing  26  and shaft  16 . Base plate  13  attaches to axle shaft end  11  along a plurality of bolts  64  extended outwardly from the axle shaft end. Bolts  64  are inserted into holes  63  through base plate  13  and the base plate is then secured to axle shaft end  11  by the attachment of nuts  66  to bolts  64 . 
     Prior to positioning base plate  13  on axle shaft end  11 , a mating disk  17  is attached to the outwardly oriented face (i.e. the face oriented away from axle shaft end  11 ) of base plate  13  by a plurality of screws  68  inserted into base plate  13  and mating disk  17  from the inwardly oriented face of foundation disk  13  toward the outwardly oriented face. The backing plate  14  formed by the assembly of the base plate  13  and the mating plate  17  then is assembled as a group onto axle shaft end  11 . 
     Magnetic plate shaft  16  is screwed at its threaded end  48  into a cooperatively threaded hole  49  in mating disk  17 . The opposite end of shaft  16  is a reduced radius end  47  onto which a magnet mounting plate  40  of magnetic plate  18  is positioned. Mounting plate  40  is retained on shaft  16  by a washer  46 , which is placed over end  47  and an opening through plate  40 . A screw  78  is then placed through the washer and into shaft  47  to pin magnetic plate  40  on shaft  16 . As described below, magnetic plate  40  incorporates a bearing allowing magnetic plate  40  to freely rotate on reduced end  47  of shaft  16 . 
     Housing  26  encloses magnetic plate  18  and magnetic plate shaft  16  upon positioning of the circumferential rim  84  defining an edge to housing  26  into a circular channel  86  in the outer face of mating disk  17 . A notch  101  is situated along the interior edge of the rim. Notch  101  provides a nesting spot for an O-ring  59  which is pressed between the faces of the notch and the interior edge of circular channel  86  to seal housing  26  against mating disk  17 . Screws  68 , inserted from inward face of base plate  13 , through the base plate and mating disk  17  into receiving holes  82  at the bottom of the circumferential rim  84  lock the housing  26  onto the backing plate  14 . Counterweight  22 , which is fixed to the inward face of magnet support plate  40 , pulls the plate to a rotational position with the counterweight or pendant vertically below shaft  16 . Backing plate  14  and shaft  16  will rotate when a wheel mounted to axle shaft end  11  rotates. Under the influence, and inertia, of the mass of counterweight  22 , magnetic plate  18  does not turn with the wheel, but remains substantially stationary with the counterweight below the (turning) shaft  16 . 
     A printed circuit board  32  is affixed to the outward oriented shell top of housing  26 . Bolts  88  are mounted through the circuit board  32  into wall  56  of housing  26  to retain the circuit board on the housing. Various circuit components  80  and electro-mechanical components, including solenoid pump  72  are mounted onto one face of circuit board  32  in a conventional manner. Solenoid pump  72  (if used) delivers pressurized air to tire pressure valves  50  along air lines  73  and  75  to channels  76  and  77 , respectively. Other types of pumps may be used, such as a magnetic button pump mentioned above. 
     Circuit board was closed within a Lexan cover  34  which fits over the circuit board and mates with the outward wall section of housing  26 . An O-ring  58 , fitted between the cover and the housing, seals the cover against the housing  26 . A plurality of screws  90  fitted through a rim to the cover  34  into housing  26  retain the cover against the housing. 
     Referring now to FIGS. 4A-B and FIGS. 5A-B, magnetic plate  18  is described in greater detail. Magnetic plate  18  is constructed on a magnet support plate  40 , which is a flattened disk shaped member with a hole  96  centered on the axis of symmetry of the disk which passes through the disk from major surface to major surface. In a preferred embodiment, eight flattened, pie section shaped magnets  38  are disposed on one face of magnet support plate  40 . Magnets  38  are arranged circumferentially around the perimeter of the major surface of the magnet support plate  40  and may be affixed thereto by gluing, or fasteners fitted through holes  94 . Magnets  38  are oriented to present a pole on their exposed surfaces oriented away from the magnet support plate  40 . The poles alternate in polarity, so that as they pass by a field coil  24  potentials of alternating polarity are produced on the coil. 
     Hole  96  is lined with an antifriction bearing  92  which fits around narrowed end  47  of shaft  16 . Magnet support plate  40  freely rotates on bearing  92 . The exterior of bearing  92  provides a support for a washer  46  used in retaining magnetic plate  18  on shaft  16 . Pendant, or counterweight  22 , is positioned on the opposite major surface of magnet support plate  40  as magnets  38 . Counterweight  22  must be sufficiently massive to prevent magnetic coupling between one of magnets  38  and a magnet piston from a magnetic button pump resulting in the magnetic plate  18  rotating with housing  26 . 
     FIG. 6 illustrates a power utilization circuit  100  which provides for the collection, conditioning and transmission of data from sensors. Separate pressure sensors  102 ,  104  are provided for each fire (not shown). A temperature sensor  106  may be placed in communication with the air within the tires to provide an indication of tire temperature. A hub temperature sensor  108 , based on an air temperature sensor within housing  26  or within cover  34 , may be provided. Conventional amplification and digital to analog conversion circuitry (signal conditioning circuits)  110  is provided for each signal. 
     The signals from each of the conditioning circuits  110  is routed through a multiplexer  112  under the control of a microcontroller  114 , which can select which signal to pass to a transmitter  116  for broadcast to a remote receiver  117  located elsewhere on a vehicle. In some embodiments transmitter  116  may be replaced with a transceiver as a CAN (controller area network) remote receiver  117 . In such cases remote commands such as to began inflation of a tire may be returned to microcontroller  114 . Microcontroller  114  may control actuation of a switch  172  which in time controls powering a solenoid pump  72 . Such signals commanding increased pressurization may come upon indication from other sources that the vehicle is carrying an especially heavy load. 
     FIG. 7 illustrates the power supply circuitry  120  used to power the utilization circuitry  100  and the solenoid pump  72 , if used. A field coil  24  is connected to a conventional rectifier  122  and filter  124  arrangement to supply voltage at a selectable level to a switching regulator  126 . Since power is rectified and filtered, the utilization circuitry remains energized regardless of the direction of movement of the vehicle. Switching regulator  126  supplies power to a 5-volt regulator  128 , which in turn powers the components of the utilization circuitry  100 . A solenoid pump  72  receives power from capacitor  124  when switch  172  closes. 
     FIGS. 8A-B illustrate two pumps usable with the invention. Magnetic button pump  42  may be used instead of solenoid pumps, reducing power demands on the power supply circuitry  120 . Magnetic button pump  42  comprises a magnetic button piston  44  retained for linear reciprocation in a cylinder  150 . A diaphragm  161  seals the piston  44  against the interior wall of cylinder  150 . Magnetic button piston  44  is retained within cylinder  150  by a lip positioned at one end of cylinder  150 . An opening  136  allows air to freely move into and out of the portion of cylinder  150  between piston  44  and the opening. Piston  44  reciprocates under the influence of magnetic poles of alternating polarity of magnets  38  passing close over opening  136 . As piston  44  is drawn toward opening  136 , air is pulled into cavity  151  through a one way check valve  130 . As piston is pushed away from opening  136  air is forced under pressure through an outlet provided by a one way check valve  132 . 
     Solenoid pump  72  is constructed similarly to button pump  42 . However, instead of magnets  38  providing reciprocation of piston  44 , a solenoid  155  wrapped on cylinder  150  effects movement of magnetic piston  44 . Indeed, in a solenoid pump piston  44  may be umagnetized iron. FIG. 9 illustrates a pressurization circuit usable with either type of pump. A pump  160  provides air under pressure to a Schrader valve  136 , to which tubing connecting the sensor assembly  10  to the tires may be provided. As illustrated a single pressure sensor  102 B, positioned in the circuit between the Schrader valve and a Y-connection splitting the delivery of air to the two tires, indicates back pressure in the system when air is delivered. A pressure sensor or situated here displays data which in effect is an average of the pressures in the two fires. Alternatively, separate sensors may be placed in each circuit downstream from check valves  140 , which prevent over pressurization of the tires. 
     The invention provides a sensor system which can be powered without use of a battery or direct external connection while mounted on a rotating wheel hub. The system returns data to a central controller and can be integrated with other vehicle control arrangements. Alternatively, a minimum system can be deployed to alert the driver of a vehicle of out of specification operation. 
     While the invention is shown in only one of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit and scope of the invention.