Sensor for a pneumatic tyre

Abstract: A sensor (1) for detecting rotations of a pneumatic tyre on a vehicle comprising two spaced apart mounting points for attachment to the radially inner surface of the tyre tread region, a contact member between the mounting points for contacting the inner surface of the tyre between the two mounting points and signal producing means adapted to produce a signal when the contact member is moved radially of the tyre relative to the two mounting points wherein damping means are provided to so that a signal is generated when the movement occurs rapidly but slow movement generates no signal so that on rotation of the tyre on a vehicle a signal is produced each time the tread region to which the sensor (1) is attached becomes change in radius at the contact patch of the tyre but when the tread radius changes slowly such as when there is a pressure change in the tyre and the movement is slow no signal is produced.

Description: The present invention relates to a sensor for a pneumatic tyre and particularly to a sensor for detecting rotations of the tyre in service and producing an output signal which can be counted to indicate the result. It has long been an objective in tyre and vehicle development to be able to effectively monitor the distance travelled by a tyre without needing to rely on the vehicle distance meter. In the European patent application published as EP-A-0 829 382 which is state of the art according Art. 54(3) EPC for all designated contracting states exept CY there is disclosed a sensor for detecting the rotations of a pneumatic tyre on a vehicle comprises a rigid base member, adapted for attachment to the radially inner surface of the tyre tread region, at least two spaced-apart mounting links, between said mounting links a force sensing member producing a countable output signal and means for processing said output signal such that on rotation of the tyre a force variation is applied to the force sensing member due to the changes in circumferential radius of curvature of the tyre tread in the contact to the road. The force measuring member is a force sensitive resistor the resistance of which is monitored by the electronic circuit. It is linked to inside of the tread region by means of a resilient link member. Document GB 2 307 044 A which is the state of the art document according Art. 54 (2) EPC for the designated state CY discloses a tyre mileage monitoring device which comprises a mechanical transducer mounted in use adjacent the periphery of a tyre of a vehicle, for providing an electrical output signal representative of mechanical forces acting on the periphery of the tyre during rotation thereof and a signal processing means for receiving the output signal of the mechanical transducer and providing an output signal representative of changes in the mechanical forces acting on the periphery of the tyre as a result of the periphery of the tyre adjacent the transducer coming into contact with the ground. Sensors of the above type, however, produce signals due to tyre inflation pressure and mounting of the sensor to give the desired sensitivity without false signalling is difficult. It is an object of the present invention to overcome the above problems and provide an improved tyre rotation sensor which makes it really practicable to measure the distance covered by a tyre. According to one aspect, the present invention provides a sensor for detecting rotations of a pneumatic tyre on a vehicle comprising two spaced apart mounting points for attachment to the radially inner surface of the tyre tread region, a contact member between the mounting points for contacting the inner surface of the tyre between the two mounting points and signal producing means adapted to produce a signal when the contact member is moved radially of the tyre relative to the two mounting points wherein damping means are provided to so that a signal is generated when the movement occurs rapidly but slow movement generates no signal so that on rotation of the tyre on a vehicle a signal is produced each time the tread region to which the sensor is attached becomes changed in radius at the contact patch of the tyre but when the tread radius changes slowly such as when there is a pressure change in the tyre and the movement is slow no signal is produced. The mounting points may be points on the inner surface of the tyre or may be points remote but attached thereto so that the points maintain a fixed relative position with respect to the inner surface. The signal may be electrical and the damping means may be mechanical or electrical. Preferably a piezo-electric device is used as the signal producing means. Such devices generate a signal only when the force is applied rapidly and no output is generated when the force is applied slowly such as when the tyre tread radius may change as the tyre is inflated. A second aspect of the invention comprises a method of counting the rotations of a pneumatic tyre on a vehicle characterised by sensing the changing radius of the tread region using a sensor mounted inside the tyre under the tread region having two spaced apart mounting points for attachment and an intermediate contact member which is acted upon by the tyre when the tyre radius is changed at the ground contact patch and damping means are provided for the sensor so that a signal is generated only when relative movement between the mounting points and the contact member occurs rapidly and not for slow movement so that on rotation of the tyre on a vehicle a signal is produced each time the tread region to which the sensor is attached enters the contact patch but when the tread radius changes slowly such as when there is a pressure change such on inflation of the tyre the movement is slow and no signal is produced. Further aspects of the present invention will be apparent from the following description, by way of example only, of an embodiment of the invention in conjunction the attached diagrammatic drawings in which: Figure 1 is a transverse cross section of a tyre with a sensor mounted on the inner surface of the tread region; and Figure 2 is a detailed enlarged view of the sensor of Figure 1. The sensor comprises a cylindrical case 1 fitted with a top closure member 2 and having a thin flexible base 3. The sensor dimensions of approximately 20 mm x 18 mm diameter. The sensor has around it an electronic pack P which will be explained later. For the present the sensor will be further described. The sensor 1 is mounted on the inner side T of the tread region of tyre. It is preferably mounted on the centreline of the tyre tread to ensure that the sensor is midway between the edges of the tread region. The sensor is attached to the tyre by a layer 4 of a suitable adhesive. One such adhesive comprises a one-component medium modulus polyurethane based fast cure adhesive, such as for example SIKAFLEX 221-A available from SIKA Limited. The thickness of the adhesive is chosen so that the fatigue life of the joint is very high bearing in mind that the tyre will flex under the sensor many thousands of times in its running life on a vehicle. A suitable thickness for the adhesive is in the range of 2 to 2.5 mm. Inside the sensor a small bar 5 of piezo electric material is adhered to the upper surface of the base 3. An electrical circuit block 6 is mounted at the top of the sensor and is connected to the piezo electric bar 5 by two wires 7. The resultant sensor has the sensing element which is the piezo electric material bar 5 effectively fixed at its two ends 5a and 5b. These points are attached through the adhesive to two spaced apart points P1 and P2 on the inner surface of the tyre tread T. The centre of the Piezo electric material bar 5 is attached to the centre of the base 3 and then to the inner surface of the tyre at a point P3 midway between the point P1 and P2. Thus when the tyre tread is flattened in the contact patch from its normal curved shape the centre of the bar 5 is moved radially inwards with respect to the fixed point at its ends. The electrical circuit block 6 processes the signal so that an output pulse is produced only for radially inward movement of the contact point. A suitable sensor is available from Diamond Electronics Ltd., Fourways Technology Park, London Road, Smallwood, Sandbach, Cheshire CW11 2US England as Everswitch Type SMF1 - AN. It is important to note that the bending when the tyre tread at the sensor enters the contract patch and is flattened is quite rapid and so an output voltage results. Also no output pulse is produced when the bar 5 is bent back to its original curvature when the sensor part of the tyre moves out of the contact patch and then all is reset to await the next rotation of the sensor into the contact patch. The signal is passed to the electronic pack which is here shown as a ring shaped container. In it a second electronic circuit (not shown)is provided at, which comprises a pulse counting unit, a radio transmitter and power supply battery. These allow the number of rotations sensed to be stored and then transmitted to a receiver external to the tyre or even external to the vehicle upon which the tyre is fitted as required. The most important feature of the sensor is that the reaction is only to rapid movement. This gives a "damping" effect to the sensor which means that it does not give false rotation signals when for example the tyre tread curvature changes due to tyre inflation. These produce only slow changes in tyre tread radius. The damping effect can of course be provided by other means including for example the use of the electrical circuit to ignore unwanted signal or even by mechanical means in a force transmission link to the signal generating means. Also other signal generating means may be utilised in place of the piezo electric material bar. Accordingly the sensor allows interrogation of the tyre as to how many deflections it has gone through and the output may be calibrated in miles or kilometres as required. As will be immediately apparent the total device inside the tyre may also include pressure, temperature and other sensors so that a set of data relevant to the particular tyre can be transmitted when required.

Claims: A sensor (1) for detecting rotations of a pneumatic tyre (T) on a vehicle comprising two spaced apart mounting points (P1,P2) for attachment to the radially inner surface of the tyre tread region, a contact member between the mounting points for contacting the inner surface of the tyre between the two mounting points and signal producing means (5) adapted to produce a signal when the contact member is moved radially of the tyre (T) relative to the two mounting points (P1,P2) wherein damping means are provided to so that a signal is generated when the movement occurs rapidly but slow movement generates no signal so that on rotation of the tyre (T) on a vehicle a signal is produced each time the tread region to which the sensor (1) is attached becomes changed in radius at the contact patch of the tyre (T) but when the tread radius changes slowly such as when there is a pressure change in the tyre and the movement is slow no signal is produced. A sensor according to claim 1 characterised in that the sensor produces a signal only for radially inward movement of the contact member. A sensor according to claim 1 or 2 characterised in that the signal producing means (5) is electrical. A sensor according to claim 1 or 2 characterised in that the damping means comprises mechanical means. A sensor according to claim 1, 2 or 3 characterised in that signal producing means (5) is a piezo-electric device which generates an electrical output when deformed rapidly but substantially no electrical output when deformed slowly. A sensor according to claim 5 characterised in that the piezo-electric device comprises a rod shaped member mounted between the two mounting points (P1,P2) and the contact member acts at the mid point of the rod shaped member. A sensor according to claim 4, 5 or 6 characterised by an electrical circuit which generates the output signal only when the rod moves radially inwards. A tyre containing a sensor according to any of claims 1 to 7 characterised in that the mounting points are arranged transversely of the tyre so that both mounting points enter the contact patch at the same time and the flattening of the tread curvature is sensed laterally of the tyre. A tyre containing a sensor according to any of claims 1 to 7 characterised in that the mounting points are arranged longitudinally of the tyre (T) so that one mounting point enters the contact patch, then the contact member and finally the second mounting point so that the flattening of the tread curvature is sensed longitudinally of the tyre. A sensor according to any of claims 1 to 9 characterised by a data storage memory enclosed in the sensor (1) to allow storage of the signals as data for later interrogation by a sensor external of the tyre. A method of counting the rotations of a pneumatic tyre on a vehicle characterised by sensing the changing radius of the tread region using a sensor (1) mounted inside the tyre (T) under the tread region having two spaced apart mounting points (P1;P2) for attachment and an intermediate contact member which is acted upon by the tyre when the tyre radius is changed at the ground contact patch and damping means are provided for the sensor (1) so that a signal is generated only when relative movement between the mounting points and the contact member occurs rapidly and not for slow movement so that on rotation of the tyre on a vehicle a signal is produced each time the tread region to which the sensor (1) is attached enters the contact patch but when the tread radius changes slowly such as when there is a pressure change such on inflation of the tyre (T) the movement is slow and no signal is produced. A method according to claim 11 characterised in that the signal is produced when the tyre (T) tread region is flattened in the contact patch. A method according to claim 11 or 12 characterised in that the signal is produced only for radially inward movement of the contact point.

Inventors: PROTTEY FREDERICK VERNON, PROTTEY, FREDERICK VERNON
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES LTD.
Application year: 1998
Main classification: B60C23
IPC codes: G01P3, B60C23