Abstract:
The present invention is directed to a wheel condition detection and signalling device. The device includes a chamber which is capable of being attached to a wheel of a truck to rotate therewith and a pendulum having significant mass and is rotatably mounted within the chamber in such a manner that the pendulum remains generally non-rotating during rotation of the chamber. The device also includes a detector means for detecting an unacceptable condition of the wheel and emitting a signal dependent upon such condition and a transmitter for transmitting that signal to a receiver. The chamber carries a wire coil which is mounted on a core having two outside parallel arms provided with end faces. The pendulum carries a series of magnets of opposite polarity, the arrangement being such that on relative rotation of the chamber and the pendulum, the magnets will pass the end faces of the coil in adjacent relationship, and that when one magnet is adjacent one end face of the coil, another magnet of opposite polarity is adjacent the other end face of the coil whereby on relative rotation of the coils and the poles, an electric current is generated in the coils to energise the transmitter.

Description:
[0001]     This invention relates to vehicles.  
         [0002]     For various reasons the conditions of the wheels or tyres of vehicles become unacceptable. The most typical of these conditions occur when the air pressure in a tyre falls below a predetermined amount. Another unacceptable condition is when the wheel becomes overheated due for example to brakes or bearings over-heating and then jamming. A further unacceptable condition occurs when there is excessive vibration of the wheels indicating a possible tread separation of the tyre.  
         [0003]     When tyres on vehicles and in particular on loaded trucks are under-inflated or flat, this causes serious wear and safety problems. In particular, riding with on a loaded truck on under-inflated or flat tyres, causes massive heat build up and distortion of the profile of the tyres. This causes excessive wear on the tyres and in extreme cases destroys the side walls and carcases of under-inflated or flat tyres.  
         [0004]     When a “flat” occurs on a side-by-side configuration, the good tyre then bears the load of both the tyres causing excessive wear on the good tyre. The two tyres bulge and run against each other causing a tremendous heat build up. If this condition persists it can result in the destruction of both tyres. This is a costly event resulting also in the down-time of the vehicle. It also represents a considerable road hazard to other road users.  
         [0005]     Furthermore there is the serious problem of large chunks of tyres (often the tread of re-treaded tyres) falling off. This can damage the host vehicle, and can result in the tyre remnants, being either thrown by the tyre into the path of oncoming traffic or just lying in the path of traffic threatening damage to vehicles on the road. Such thrown-off tyre chunks may also snag and damage the brake lines of the host vehicle resulting in brake failure. In addition the loss of parts of the tyre will cause unacceptable vibration of the wheel. The shredded tyres and expired casings also impact detrimentally on the environment.  
         [0006]     It will be appreciated that tyres, and in particular tyres used on trucks and busses and lorries are extremely expensive items. Thus the destruction of a tyre has serious economic as well as safety consequences. In addition, if one or more tyres are deflated, this will cause increased drag on the vehicle which will result in increased fuel consumption and consequent increased cost in the running of the vehicle in question.  
         [0007]     It follows that it is highly desirable to provide a wheel condition detection and signalling device (WCDSD) which will give a warning when there is an unacceptable condition of a wheel or tyre. Numerous deflation detectors (which are one type of WCDSD) have been proposed to provide the driver of a vehicle with a warning that one or more tyres is/are under inflated. Many of these detectors are required to transmit a signal on detection of under-inflation to a receiver in the cab of a truck so that the driver is aware of the condition. A significant requirement of such detectors is the provision of electrical power to power the detectors and transmitters. Clearly the use of batteries alone which have a finite life are not entirely satisfactory because they do not allow for constant signals or the continuous computerisation of data relating to the host vehicle.  
         [0008]     A number of tyre deflation detectors have been proposed.  
         [0009]     On the face of it these are usually theoretically capable of working. However it has been found that such devices are in most cases not sufficiently robust to withstand the various forces that are incurred at the axle of a truck and consequently the detectors fail. Alternatively the cost of manufacturing the detector become prohibitive. Furthermore it has been found that the power generated at the generator described above is often, if not usually, less than the requisite power for operating the transmitter to transmit the signal to the receiver. It is critical that the signals of one system do not interfere with those of another: yet it is also necessary to inter-change trailers without any manual settings being implemented to effect the change. No detection device that is capable of a fully automatic change-over of trailers has been found. Furthermore, it has been found that many detection devices are limited in the number of wheels that they can accommodate in the host vehicle with a maximum of 20 wheels being a typical limitation.  
         [0010]     Typical of arrangements above described are to-be found in South African Patent No 97/6722 (corresponding to U.S. Pat. No. 6,046,672); U.S. Pat. No. 4,229,728 1997 (Tremba); U.S. Pat. No. 4,075,603 (Snyder); and U.S. Pat. No. 4,536,668 (Boyer) and European Patent 0 563 723 (Eurafrica Videomatic S.r.l.).  
         [0011]     An attempt is made to overcome these problems in a new arrangement which embodies the invention.  
         [0012]     According to one aspect of the invention there is provided a wheel condition detection and signalling device comprising:—
        a chamber which is capable of being attached to a wheel of a truck to rotate therewith,     a pendulum having significant mass and being rotatably mounted within the chamber in such manner that the pendulum remains generally non-rotating during rotation of the chamber,     detector means for detecting an unacceptable condition of the wheel and emitting a signal dependant upon such condition     a receiver for receiving signals from other components of the system and     a transmitter for transmitting that signal to a receiver 
 
 wherein 
    the chamber carries a coil, and conveniently two coils, which is mounted on a core having two outside parallel arms provided with end faces and     the pendulum carries a series of magnets of opposite polarity, 
 
 the arrangement being such 
    that on relative rotation of the chamber and the pendulum, the magnets will pass the end faces of the coil in adjacent relationship, and        
 
         [0021]     that when one magnet is adjacent one end face of the coil, another magnet of opposite polarity is adjacent the other end face of the coil, so that on relative rotation of the coils and the poles, an electric current is generated in the coils.  
         [0022]     The power from the coils may be used to power the transmitter directly or, and preferably, it is used in conjunction with battery means which provides power during very slow movement of the wheels, say less than 50 to 55 rpm and/or at a vehicle speed of less than about 10 kph. Preferably such battery is a rechargeable battery which is recharged by such power when the wheel is rotating above the said number of revolutions or the vehicle is travelling faster than the said speed. More than one battery may be used.  
         [0023]     The magnets are preferably arranged in a circle on the pendulum centred on its axis of rotation and having a diameter approximately equal to the distance apart of the centres of the end faces of the coil.  
         [0024]     There are preferably a “double odd number” (as defined below) of the magnets. By the term “double odd number” as used herein is meant an even number which when divided by two gives an odd number. The preferred number of magnets is six. The magnets are preferably arranged with their polar axes parallel to the axis about which the pendulum swings.  
         [0025]     The pendulum conveniently comprises an annular part rotatably carried by a bearing and an eccentric weight projecting therefrom. The annular part carries the magnets on one face thereof. The eccentric weight preferably comprises lead or other heavy material and has a mass of between 200 gm and 500 gm and preferably between 320 gm and 360 gm and more preferably about 340 g. The weight is preferably bolted on to a member projecting from the annular part. The annular part further comprises a substantially cylindrical bearing carrier within which the bearing is received.  
         [0026]     This bearing carrier preferably has inwardly directed means at its mouth or open end. The bearing carrier is capable of being resiliently distorted to permit the bearing to enter the said carrier, the arrangement being such that when the carrier returns from the distorted position, the inwardly directed means extends into the path of the bearing to prevent or inhibit it from being removed from the said bearing carrier. Further distortion of the bearing carrier after the insertion of a bearing is prevented by attaching a ring around the circumference of the bearing carrier. The bearing carrier is preferably provided with a plurality of pairs of closely spaced cuts or slots that define between them arms which can resiliently swing outwardly. The inwardly directed means are provided at the ends of the said arms. Reinforcing gussets, are preferably provided inbetween the cylindrical member and the annular member.  
         [0027]     Where the unacceptable condition is a low tyre pressure, a pressure detection means is preferably incorporated in a chamber which is capable of being connected to a tyre to be subject to the pressure therein. A pressure detector is preferably provided within the chamber and is connected to the electrical means. The pressure detector is preferably mounted on the board, preferably a PCB, on which the electrical means is carried. A heat conductor is also preferably provided having a part projecting into contact with the part of the wheel and another part in direct or indirect communication with a heat detector connected to the electrical means. In addition the device preferably further comprises a vibration detector. The vibration detector conveniently comprises a cylinder with a movable clapper therein.  
         [0028]     Additional or other detector means may be provided.  
         [0029]     The device may with advantage be used on the wheels of a heavy duty vehicle such as a truck, bus, or taxi and also the wheels of a railway carriage. 
     
    
       [0030]     An embodiment of the invention will now be described by way of example with reference to the accompanying drawings.  
         [0031]     In the drawings:— 
         [0032]      FIG. 1  is a perspective view showing a wheel condition detection and signalling device of the invention in place on a wheel of a truck,  
         [0033]      FIG. 2  is a section on line  2 - 2  of  FIG. 1 ,  
         [0034]      FIG. 3  is an enlarged detail section along the diameter of the device,  
         [0035]      FIG. 4  is a detail section through the device along a diameter at right angles to that on which  FIG. 3  is taken,  
         [0036]      FIG. 5  is a perspective view from the above of the outer side of the device housing,  
         [0037]      FIG. 6  is a perspective view from below of the inner side of the device,  
         [0038]      FIG. 7  is a view showing the PCB mounted on the outer housing part,  
         [0039]      FIG. 8  is a perspective from below of the inner part of the device,  
         [0040]      FIG. 9  is a cut-away perspective section through the inner part of the housing showing the pendulum in position,  
         [0041]      FIGS. 10 and 11  are perspective views of the pendulum arrangement from opposite sides,  
         [0042]      FIG. 12  is a perspective view of the pendulum,  
         [0043]      FIGS. 13, 14  and  15  are respectively front, side and rear views of the pendulum,  
         [0044]      FIGS. 16 and 17  are respectively sections on lines  16 - 16  and  17 - 17  of  FIG. 13 ,  
         [0045]      FIG. 18  is a section through a bearing pin on which the pendulum is rotatably mounted,  
         [0046]      FIG. 19  is a perspective view of the heat guide,  
         [0047]      FIG. 20  is a perspective view of the bracket on which the device is carried,  
         [0048]      FIG. 21  is a perspective view, partially broken away, of the vibration device. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0049]     Referring now to  FIG. 1  there is shown a wheel condition detection and signalling device (WCDSD)  10  of the invention. The WCDSD  10  is mounted on each wheel drum of a truck (including the “horse”). Some (and indeed most) of the wheel drums carry a pair of wheels and tyres. The WCDSD  10  is capable of working with such an arrangement as well as where the wheel drum carries a single wheel and tyre as is shown in the drawings.  
         [0050]     This WCDSD  10  comprises a control casing  100  mounted on a carrier bracket  200  carried by a wheel  300  of a truck.  
         [0000]     The Carrier Bracket  
         [0051]     The carrier bracket  200  (best shown in  FIG. 20 ) is a sheet steel pressing comprising a central land  202  carried by six legs  204  having outwardly directed feet  206  at their ends. Each foot  206  has an opening  208  therethrough. These feet  206  rest on the flange  302  of the dust cap  304  of the wheel  300 . Stub bolts (not shown) are provided to secure the dust cap  304  to the wheel  300 . Each alternate bolt passes through an opening  208  in a foot  206 . Nuts (not shown) engaging the bolts  306  secure the bracket  200  to the wheel  300 .  
         [0052]     A number of openings  210 ,  212  and  214  are formed in the land  202 . These openings will be described more fully below as will be the way in which they are used.  
         [0000]     The Control Casing  
         [0053]     The control casing  100  comprises an outer casing part  102  (shown in detail in  FIGS. 5 and 6 ) and an inner casing part  104  (shown in  FIGS. 7 and 8 ). The casing parts  102  and  104  are plastics mouldings preferably comprising Nylon 6/6 with a 30% glass fibre filling.  
         [0054]     The outer casing part  102  (see  FIGS. 5, 6  and  7 ) is of circular section, is slightly domed and has a dependent peripheral skirt  112 . Internally the casing part  102  has radially extending reinforcing ribs  114  which radiate from a central annulus  116  via an intermediate circular support  118  to an end member  120  adjacent the skirt  112 . Small bosses  122  are provided slightly inboard of the skirt  104 , each having a projecting top part  124 . The bosses  122  are equi-spaced on a circle coaxial with the casing part  102  midway between the support  118  and the end member  120 .  
         [0055]     Externally the upper part  102  has a pair of upstanding hollow bosses  126  near its periphery at diametrically opposed locations. Each boss  126  has an internal crosspiece  128  through which is a central aperture  130  (best seen in  FIG. 3 ).  
         [0056]     The inner part  104  (see  FIGS. 8 and 9 ) comprises a deep dished part  132  having a cylindrical wall  134  and a flat base  136 . An outwardly directed flange  132  extends from the end of the wall  132  and ends in a cylindrical rim  140 . The rim  140  is twice as thick as the skirt  112  and its inner portion forms a lip  142  which, when the two casing parts  102  and  104  engage together, lies inside the skirt  112 .  
         [0057]     Externally the inner casing part  104  is provided with reinforcing gussets  144  which extend between the outside of the cylindrical wall  132  and the flange  138 . The gussets  144  are arranged in pairs. A pair of upstanding hollow bosses  146  is provided at diametrically opposed locations, each between two pairs of gussets  144 . Each boss  146  has an internal crosspiece  148  in which is a central aperture  150  in the same way as the bosses  126 .  
         [0058]     Between the gussets  144  of each pair is an aperture  152  through the flange  138 . Each aperture  152  is continued, on the inner face of the flange  138 , in a boss  154  having a countersunk end, the diameter of which is such that the top parts  124  of the bosses  122  are interference fits therein.  
         [0059]     The flat base  136  has a central slightly countersunk aperture  156  surrounded by a circle of eight bores  158  the ends of which have hexagonal countersunk portions  160 .  
         [0060]     Located between the casings  102  and  104  is an internal divider in the form of a disk shaped PCB  162 . Near the periphery of the PCB  162  is a series of apertures at such location that the projecting parts  116  of the bosses  114  pass therethrough to engage in the bosses  154  of the lower casing part  104 . Bolts (not shown) pass through these apertures to hold the two casing parts together.  
         [0061]     At positions corresponding to the positions of the bosses  126  and  146  there are provided on opposite sides of the PCB  162  a pair of hollow nylon cylinders  164  forming pressure chambers which are connected by small apertures (not shown) through the PCB  162  so that their interiors are at the same pressure. The cylinders  164  have flanges  166  by means of which they are bolted together by bolts  168  passing through the flanges  166  and the PCB  162 . Suitable O-ring sealing means  170  are provided to ensure that the pressure chambers are properly sealed. Each cylinder  164  carries a pressure valve  172  that projects through the apertures  126  and  154 . Within one cylinder  164  of each pair is a pressure sensitive device  174  connected to the electric circuit located below a metal bridge member against which the valve  172  butts and is in electrical contact therewith.  
         [0062]     Carried on the lower part of the PCB  162  is a circuit incorporating a transmitter and receiver as well as a battery set  176 . The circuit is connected by wires to the bridge member so that by connecting a crocodile clip to each valve  172  electric power may be supplied to the PCB  162  and also to the battery set  176  for any desired requirement such as e.g. reformatting the transmitter or recharging the batteries.  
         [0000]     Power Generating Apparatus  
         [0063]     Within the dished part  130  there is contained apparatus for generating electric power. This apparatus comprises a coil arrangement  180  and a pendulum arrangement  400  to be described.  
         [0064]     The coil arrangement  180  comprises two coils  182  and  184  mounted respectively on the arms  186  of a “C”-shaped laminated core  188  and being carried by mandrels  190  mounted on the underside of the PCB  162 . The mandrels  190  have the legs  192  which are bolted to the PCB  162  and have wires (not shown) from the coils connecting to the electric circuit.  
         [0065]     The end faces  194  of the arms  186  of the core  188  are flat.  
         [0000]     The Pendulum Arrangement  
         [0066]     The pendulum arrangement  400  comprises a pendulum  402  and an eccentric weight  404 .  
         [0000]     The Pendulum  
         [0067]     The pendulum  402  is a plastic moulding. It comprises an annular portion  406  with an enlarged central aperture  408  and arcuate projection  410 . This projection  410  subtends an angle of about 80° at the centre of the main portion  406 . It serves to carry the pendulum weight  404  as will be described below.  
         [0068]     The main portion  406  comprises a flat floor  412  with a cylindrical bearing housing  414  of smaller diameter rising therefrom. Equi-spaced on a circle centred on the axis  416  of the housing  414  are six bosses  418  with blind bores  420  respectively therein. The axes of the bosses  418  are parallel to the axis  416  of the main portion  406 . The diameter of the circle is about the same as the distance apart of the centres of the end faces  194  of the arms of the core.  
         [0069]     Radially extending triangular gussets  422  extend from the housing  414  to the floor  412 . At their upper ends, each gusset is cutaway at  422  leading a vertical surface  424  of the housing. Six pairs of closely spaced cuts  426  are provided in the housing  414  between gussets  422 . These cuts  426  extend from the top of the housing  414  to form thin arms  428 . At its upper end, each arm  428  is provided with an inwardly directed lip  430 , the upper surface  432  of which slopes downwardly towards its free end. The under surface of each lip  430  extends in a plane normal to the axis  416  of the main portion  406 . The arms  428  are capable of swinging outwardly for the purpose which will be described.  
         [0070]     Cast into the main portion  412  is a flat steel insert member  436  (see  FIG. 16 ) comprising an annulus  438  having an aperture  440  which is of slightly less diameter than the inside diameter of the aperture  408 . Six arms  442  project radially from the annulus  438  and form part of the bases of the blind bores  420 . Two small escape holes  444  are provided through the edges of the arms  440  and through the main portion the base of each boss  418  to provide escape openings as will be described. A narrow flat lip  446  (see  FIG. 17 ) projects above the annulus.  
         [0071]     Six cylindrical magnets  448  are provided having their polar axes coaxial with the cylinder i.e. the poles at their ends. They are inserted into the bosses  416  with the projecting ends of alternate magnets being of opposite polarity. The inner ends of the magnets  448  butt against the insert member  436  which provides a magnetic flux path for the magnets  448 . The magnets  448  are held in position by bonding agents. Excess bonding agent escapes through the escape holes  444  when the magnets are inserted into the bosses  416 .  
         [0072]     A roller bearing  450  is located in the housing  414 . The outer race  452  seats on the lip  446  which spaces it from the insert member  436 . On insertion of the bearing  448 , the outer race  452  acts on the inclined outer surfaces  430  to force of the arms  428  outwardly thereby permitting the outer race  452  to enter into the housing  414 . When the bearing  450  is homed into the housing  414 , the arms  428  swing backward and the lips  430  lie over the outer surface  436  of the outer race  452  holding the bearing  450  firmly in place. A steel securing ring  458  is placed over the gussets fitting into the cutaway portion  422  and encircling the vertical surfaces  422  to prevent the arms  428  swinging outwardly. Three equi-spaced apertured lugs  460  project from the periphery of the ring  458 . Screws  462  passing through these lugs  462  engage in the ends of three vertical columns  464  to hold the securing ring  458  in position.  
         [0000]     The Pendulum Weight  
         [0073]     The pendulum weight  404  (best shown in  FIGS. 10 and 11 ) has a mass of approximately 340 gm. It is generally in the shape of a portion of a segment being an extension of the arcuate projection  410 . The weight  404  is generally in the shape of a portion of the segment subtending 80° at the centre of the pendulum. It, the weight  404  is substantially “L” shaped in section having a main deep arcuate portion  466  with a radial inwardly directed leg  468 . This leg  468  is received in and can rotate relatively to the casing. Large axially directed countersunk bores  470  are provided through the portion  410 . The portion  466  rests against the lower face of the projection  410  of the pendulum  402 . The heads of the countersunk bores  470  receive the screws  472  holding the weight to the pendulum.  
         [0000]     The Bearing Pin  
         [0074]     The bearing  450  is carried on a bearing pin  474 . The bearing pin  474  (see  FIG. 12 ) has a cylindrical shaft  476 , which has a co-axial blind bore  478 , and fits into the inner race  450  of the ball bearing  450 . A screw  482  is threaded into the bore  478  having its head  484  acting on the outer face of the inner race  480  through a washer  486 . A flange  488  of the bearing pin  474  rests on the central land  202  of the bracket  200 . It has a central projection  490  which passes through the central opening  210 . Internally threaded blind bores  492  are provided on the underside of the flange  488 . Screws passing through the openings  212  secure the bearing pin  474  to the land  202 . It will be appreciated that as the bracket comprise metal it will serve as a heat sink for the bearing pin  474  and also will remain rigid during normal and excessive heating of this part.  
         [0075]     It will be appreciated that when mounted on the wheel, the axis  416  of pendulum arrangement will be horizontal.  
         [0076]     It will be seen therefore that as the wheel  300 , and with each of them the WCDSD  10 , rotates about a horizontal axis, the pendulum  402  carrying the heavy counterweight  404  will remain substantially stationary. Thus the end faces  194  of the coils  182  and  184  will pass by the magnets  448  which will induce an electrical current into the coils  182  and  184 . Such electrical current will serve to provide power for the PCB and the programmable integrated circuit (incorporating the transmitter carried thereby. It will be noted that when any magnet is opposite one arm of the core, the magnet opposite the other arm would be of the opposite polarity.  
         [0000]     A Heat Detector  
         [0077]     A heat detector  600  is provided. It comprises a bent sheet metal heat guide  602  (see  FIG. 19 ) having a short leg  604  at one end and a wider slightly longer leg  606  at the other end. The guide  602  is received in an axial slot  196  in the wall  134  (see  FIG. 9 ). The short leg  606  extends on the outside of the base plate  136  of the dished part  132  and is bent to lie flat thereagainst. It is clamped by the base plate  136  against the land  202  of the bracket which serves as a heat sink. The other leg  604  is screwed to a projection of the lower part close to the PCB  106  and is connected to a heat sensor  610  on the PCB. The heat sensor in turn is connected to the programmable integrated circuit or microprocessor. Should the temperature of the wheel increase beyond a certain amount, the heat transferred by the heat guide  602  to the heat sensor  610  will increase beyond a predetermined amount. The microprocessor will recognise this as an unacceptable situation.  
         [0000]     Vibration Detector  
         [0078]     At the centre of the PCB  162  in the outer casing  102  there is a vibration detector  500  (see  FIG. 21 ). The vibration detector  500  comprises a metal cylinder  502  and a clapper  504 . The cylinder  502  is secured to the PCB  162  and is connected to an appropriate electronic member (not shown). The clapper  504  has a heavy head  506 . It is located centrally of the cylinder  502  and is capable of swinging when the wheel is subjected to vibration. The clapper  504  is connected to another electronic member. Should the wheel vibrate, the clapper  504  will swing and make contact with the cylinder  502 , this will complete the circuit between the two electronic members which will convey this information to the microprocessor. Should the vibration be due to road irregularities then the vibration will be arbitrary and will be recognised as such by the microprocessor. However if the tyre on the wheel should shed some tread, the vibration would be cyclical. This will be recognised by the microprocessor as an unacceptable condition.  
         [0000]     Pressure Connectors  
         [0079]     A short copper or reinforced rubber pipe (not shown) having suitable connectors (not shown) at its ends is connected to the valve of the tyre and one valve  172 . Thus the interior of the appropriate pressure chambers are subject to the air pressure in the tyre. The pressure gauges  174  within the interiors are therefore subject to the air pressure of the tyre to which it is connected. The pressure gauge  174  is connected to the microprocessor. Accordingly should the pressure in a tyre fall below a predetermined pressure, the microprocessor will recognise this as an unacceptable condition.  
         [0080]     The tyre can be inflated through the other valve  172  of the pair.  
         [0081]     If the wheel drum carries two tyres, then the valve of the second tyre will be connected to one of the valves  172  of the other pair of valves.  
         [0000]     Operation  
         [0082]     The microprocessor is arranged to activate the transmitter to send an appropriate signal when it, the microprocessor, detects an unacceptable condition as described above. A receiver (not shown) to receive such a signal is normally provided in the cabin of the truck. This is capable of indicating the particular unacceptable condition and identifying the wheel or tyre to which it applies. Thus the driver will be aware of any unacceptable condition as soon as it arises.  
         [0083]     As mentioned, the coil provides electric power to the electronic circuitry on the PCB. It will be appreciated that when the vehicle is stationary or is moving extremely slowly no or not enough power will be generated in the coils for this purpose. The batteries  176  will now supply the appropriate power. A field effect transmitter is provided in the circuity and is arranged so that once an adequate amount of power is being generated by the coils, power will be supplied by the coils through the batteries. Thus no more current will be drawn from the batteries and more than adequate power is provided by the coils. When the coils are supplying power, they also serve to recharge the batteries. Thus the batteries will have a long life. Also there will be constant power supplied by the coils when the vehicle is travelling.  
         [0084]     The microprocessor further may incorporate a receiver which can receive a signal from a tag inserted into a tyre. This information can be transmitted to the receiver and in due course downloaded into a main computer used by the transport operator. This data may be used to give information about what distance any particular tyre has travelled irrespective of on what vehicle it has been mounted. It will also provide information about unauthorised swapping or rotating of tyres.  
         [0085]     It has been found that the generator system comprising the coil and pendulum arrangement as described above produces enough power for the circuitry and the microprocessor and in particular the transmitter. However should the device be placed on the wheel of a multi trailer unit, the transmitter may not have a long enough range to transmit signals to the receiver in the cabin of the truck or there may be too much interference to transmit the signal over this distance. To overcome this difficulty, each trailer unit may be provided with a wire connector leading from the rear of the unit to the front. At the rear of the unit there may be a receiver connected to the wire. A transmitter is connected to the front end of the wire. Thus the signal can be transmitted through such wires over a great distance to the receiver in the cabin. Alternatively such signal can be supplied by a “daisy chain” of transmitters and receivers at each of the trailers.  
         [0000]     Miscellaneous  
         [0086]     It has been found that the arrangement of the magnets on the pendulum and their arrangement relative to the faces of the coil provides a very satisfactory electrical generator which can generate adequate power for the transmitter even at relatively low rotational speeds of the wheels. Typically it can operate satisfactorily even at as low revolutions as 50 to 55 rpm (which with a one metre diameter tyre is equivalent to 10 kilometres per hour).  
         [0087]     By having the pressure detectors within the pressurised chambers damage to the detectors that occurs in arrangements where a pipe is connected directly to the detectors is obviated.  
         [0088]     The power generated as aforesaid may be put to additional purposes. For example, the number of revolutions which the tyre makes can be ascertained by counting the number of pulses generated by the magnets passing the ends of the coil. This number must the divided by the number of magnets to indicate a number of revolutions.  
         [0089]     It will be seen that overall the arrangement as above described works extremely satisfactory in giving signals to the driver as to unacceptable conditions. Thus the driver is able to take remedial action quickly which prevents more serious conditions occurring.  
         [0090]     It will be seen that if a differential gear should fail and lock or a wheel bearing seizes or a brake should instantaneously lock, the number of revolutions of the wheel will be reduced or even ceased. This condition will be detected by comparing the revolutions of all the wheels to see that which is not rotating.  
         [0091]     In another example, a scanner system may be provided for determining the tyre wear. The scanner may be arranged to detect the length of the road over which the truck passes. The microprocessor will calculate the number of revolutions that the wheel completes when passing over this length of road. The microprocessor can thus determine the circumference of the tyre and hence the diameter of the tyre. After the tyre has worn the diameter of the tyre decreases and hence the wear of the tyre tread can thus be calculated by the microprocessor. Should the wear be too great this will be detected as an unacceptable condition and treated as mentioned above. In order that extraneous conditions do not affect this operation, it is preferably best effected when the truck commences its journey and is moving slowly.  
         [0092]     The invention is not limited to the precise constructional details hereinbefore described and illustrated in the drawings. For example the device may be modified to detect unacceptable conditions on railway wheels. Here the unacceptable conditions would be excessive heat, excessive vibration and excessive wear of the periphery of the wheel. Railway units can be extremely long. Therefore the wire arrangements mentioned above (i.e. a wire extending along the length of each truck and having a receiver at the rear end and transmitter at the front end or the daisy chain”) may be essential for signals to reach a receiver in the driver&#39;s cabin in the traction unit.