Sensor for a pneumatic tyre

Abstract: A sensor for counting the rotations of a pneumatic tyre on a vehicle comprising a rigid base member (1), adapted for attachment to the radially inner surface (I) of the tyre tread region, at least two spaced-apart mounting links (4), between said mounting links a force sensing member (2) 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.

Description: The present invention relates to a sensor for a pneumatic tyre and particularly to a sensor for measuring the number of rotations of the tyre in service and producing an output signal indicating the result. It has long been an objective in tyre and vehicle development to be able to effectively monitor a tyre's condition, particularly its pressure and distance travelled. Tyre pressure monitoring has been approached by various means including the use of a detector unit mounted integrally with the tyre which transmits on demand, or in some cases continuously, a tyre pressure signal. Such a detector unit is known from US-A- 4,862,486. It is an objective of the present invention to provide a sensor and means of sensing for the number of rotations of an individual tyre which may if required be incorporated in the tyre pressure sensor mounted integrally with the tyre. Accordingly one aspect of the present invention provides a sensor for counting the rotations of a pneumatic tyre on a vehicle as set out in Claim 1 The sensor may be an electronic component and then the signal processing unit is an electronic circuit. The electronic circuit preferably includes a transmitter and a memory to store the output signal. The transmitter may operate continuously in use of the vehicle or upon receiving an interrogation request from an external detector. A preferred force sensing member comprises a force sensitive resistor, the resistance of which is monitored by the electronic circuit. The invention also includes a tyre characterised by a sensor for counting rotations of the tyre as above. According to a final aspect of the invention, the invention comprises a method of counting the rotations of a pneumatic tyre on a vehicle as set out in claim 7. 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 shows a sensor mounted on the inner surface of the tyre; Figure 2 is a plan view of a sensor from the tyre. As seen in Figure 1 the sensor comprises a rigid base member 1 which is rectangular having dimensions approximately 38mm x 33mm. Attached to the centre of one side of the rigid base member 1 is a force sensing member 2 which comprises a force sensing resistor which is a disc having a diameter of 7-8mm and a thickness of about 0.5mm. The force sensing resistor is connected to an electronic circuit (not shown) mounted on the rigid base member which monitors the resistance of the force sensing resistor. Additional electronic components are provided to give a counter which counts the number of times the force sensing resistor moves through a give pre-set resistance threshold caused by applied force which will be described below. A resilient link member 3 which comprises a dense foam material is bonded to the force sensing resistor 2. The cross section of the link member 3 is chosen to suit the sensing area of the force sensing resistor. A suitable force sensing resistor is sold by Interlink under Code Number FSR 149, although other such devices may be used. The sensor is mounted on the inside I of a tyre underneath the tread region. It is mounted with the longer 38mm long side extending in the circumferential direction of the tyre tread centreline and preferably is mounted on the centreline of the tyre tread to ensure that the sensor is away from the edges of the tread region. The sensor is mounted on the inner liner of the tyre by four approximately 10mm diameter links or pillars 4 of adhesive comprising a one-component medium modulus polyurethane based fast cure adhesive, such as for example SIKAFLEX 221-A available from SIKA Limited. The adhesive pillars 4 are made to be of a sufficient length so that the dense foam adhesive link member 3 is in contact with the inner surface I of the tyre with the tyre in its normal non-inflated, non-deflected condition. A convenient way of arranging the adhesive pillars 4 to be of this length is to provide on the radially outer surface of the link member 3 a self-adhesive surface which sticks to the liner of the tyre when the sensor is attached thereto and locates the sensor until the adhesive cures. In the resultant assembly the force sensitive resistor is in a substantially non-loaded condition when the tyre has its normal curvature. In use of the vehicle as the tyre enters and leaves the contact patch to the road the radius of curvature of the circumferential centreline of the tyre is increased due to the flattening of the tyre against the road. This causes a compressive force to be applied to the force sensing resistor 2 due to the reduction in the spacing of it from the inner surface of the tyre. Excessive compressive force which could unduly strain the adhesive pillars 4 is prevented by compression of the link member 3. Thus each time the tyre rotates and the sensor goes through the contact patch a force is applied to the force sensing resistor causing its resistance to change and the electronic circuitry counts the number of such deflections. The count is stored in a memory and either transmitted to a receiver mounted on the vehicle or more preferably transmitted to an external sensor located a small distance from the tyre but external thereto and giving the count when requested by the external device. Accordingly the sensor allow 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 rigid base member may also include pressure, temperature and other sensors so that a set of data relevant to the particular tyre can be transmitted when required. The link member 3 may be of any suitable resilience chosen so as to transmit sufficient compression force for the sensor utilised to give a countable change.

Claims: A sensor for counting the rotations of a pneumatic tyre on a vehicle comprising a rigid base member (1), for attachment to the radially inner surface (I) of the tyre tread region by at least two spaced-apart mounting links (4), between said mounting links a force sensing member (2) mounted on the base member (1) and a resilient link member (3) to link the force sensing member to the inside of the tread region 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 to produce a countable output signal and means for processing said output signal A sensor according to claim 1, characterised in that the sensor is an electronic component and a signal processing unit is provided on the base member (1). A sensor according to claim 2, characterised by an electronic data transmitter mounted on the base member (1). A sensor according to claim 2 or 3, characterised by data storage memory on the base member to allow storage of data for later interrogation by a sensor external of the tyre. A sensor according to any of claims 2-4, characterised in that the force sensing member (2) comprises a force sensitive resistor, the resistance of which changes with force applied to the resistor. A tyre comprising a sensor for counting rotations of the tyre in service on a vehicle according to any of claims 1-5. A method of counting the rotations of a pneumatic tyre on a vehicle characterised by using a force sensor mounted on a rigid base member which is attached to the radially inner surface of the tread region of the tyre at two points circumferentially in front of and behind the sensor, and a resilient link member to transmit force from the inner surface of the tyre tread to the force sensing member to sense movement of the inner surface of the tyre tread region when the tread region passes through the tyre contact patch on the road, taking a countable signal from the sensor, counting said signals to produce a result equivalent to the number of rotations of the tyre and transmitting the results to a display. A method according to claim 7, wherein the force sensor is a force sensitive resistor, the countable signal is produced as a variation in resistance and electronic circuit means mounted on the rigid base are used to produce the results.

Inventors: PROTTEY FREDERICK VERNON, PROTTEY, FREDERICK VERNON
Applicants: SUMITOMO RUBBER IND, SUMITOMO RUBBER INDUSTRIES LTD.
Application year: 1997
Main classification: B60C23
IPC codes: B60C23, G01P3, G01L17, G01C22