GB2543814A

GB2543814A - Tyre tread depth measurement

Info

Publication number: GB2543814A
Application number: GB1519166.1A
Authority: GB
Inventors: Beal Charles
Original assignee: Bartec Auto Id Ltd
Current assignee: Bartec Auto Id Ltd
Priority date: 2015-10-30
Filing date: 2015-10-30
Publication date: 2017-05-03
Also published as: GB201519166D0

Abstract

The invention relates to tyre tread depth measurement, and in particular to a tyre tread depth measurement apparatus, and a method for operation thereof. A tread depth measurement apparatus 10 is provided for measuring a tread depth of a tyre 20. The apparatus 10 comprises a body 12 having a measurement device 22 for measuring the tread depth. The body 12 further includes an electronic sensor device 28 to determine an orientation of the measurement device 22 relative to a rolling surface 18 of the tyre 20 to provide the tread depth measurement substantially along a normal (40, figure 3) to the rolling surface 18. The electronic sensor device 28 may be: an inductor circuit using inductor values, eddy current losses, Q factors; magnet; capacitor circuit may have a colpitts oscillator; light level sensor circuit; at least one photomicrosensor in a circuit, measuring displacement of a pin, they may surround the measurement device 22; a strain sensor circuit to sense deformation. The circuits may sense a proximity to metal, rubber or the tyre in general. The body 12 may include lights (36, figure 2) for illumination of the tire 20.

Description

Tyre Tread Depth Measurement

Technical Field

The invention relates to tyre tread depth measurement, and in particular to a tyre tread depth measurement apparatus, and a method for operation thereof.

Background

Tyre replacement garages are typically required to measure tyre tread depths for safety and legal reasons. Most countries specify a legal requirement for a minimum tread depth, which is linked to safety. In the UK the law requires that car tyres have a minimum tread depth of 1.6mm in a continuous band around the central three quarters of the tyre. Another reason for tyre replacement garages to measure tyre tread depth may be to improve sales. For example, a customer may choose to replace tyres when they are close to the minimum legal requirement. Typically vehicle drivers or operators prefer to maintain their tyres with more than the legal minimum for improved safety and performance in poor road conditions.

Vehicle fleet operators with large fleets of cars, vans or lorries may also require the depth of tyre treads to be known across the fleet of vehicles. Such operators may have a legal obligation to maintain the tyres of the vehicles with a certain tread depth. Cost is an important factor when operating large fleets of vehicles, and the replacement of tyres before they have worn out may represent a significant additional operation cost to the vehicle fleet operator.

It is known to measure a tyre tread depth using a pin coupled to a mechanical gauge. The pin is sufficiently small to fit into the tyre tread and the mechanical gauge measures a distance between a rolling surface of the tyre and a deepest point of the tread. It is also known to use non-contact ways of measuring tread depth such as an apparatus using a laser rangefinder or laser triangulation. The Vehicle and Operator Services Agency (VOSA) in the UK require the remaining tread depth to be measured to an accuracy of +/-0.1mm, and in some cases +/-0.01mm. A problem with the known tread depth measurement devices is that they may not be able to measure to the required accuracy, and may be susceptible to user error.

It is also known to measure a tyre tread depth using a pin coupled to an electronic gauge, which may use a Vernier measurement technique. Whereas such a device may be capable of providing the required accuracy of measurement, it is still susceptible to user error. For example, the user may not be able to see sufficiently well to locate the pin in the tread groove.

Another source of inaccuracy when using the known tyre tread depth measurement devices is that the user may place the device at an angle to the rolling surface so that it does not measure the tread depth accurately. Whereas known tyre tread depth measurement devices typically have a flat front face to assist with orientation of the device, user error is still common and may result in the tread depth reading being too large.

It is broadly an object of the present invention to address one or more of the above mentioned disadvantages of the previously known ways of tyre tread depth measurement.

Summary

What is required is a way of measuring tyre tread depth, which may reduce or minimise at least some of the above-mentioned problems.

According to a first aspect of the invention, there is provided a tread depth measurement apparatus for measuring a tread depth of a tyre, comprising a body having a measurement device for measuring the tread depth, wherein the body further includes an electronic sensor device to determine an orientation of the measurement device relative to a rolling surface of the tyre to provide the tread depth measurement substantially along a normal to the rolling surface.

Such an apparatus provides the advantage that the tread depth can be measured to an improved accuracy, for example up to an accuracy of +/-0.01mm or better. Such an improved accuracy is provided by the electronic sensor device which is able to assist with positioning the body so that the measurement device measures along the normal to the rolling surface. The Applicant has discovered that non-normality of the measurement device is an important source of inaccuracy, and may occur when the body is not in full and close contact with the rolling surface of the tyre. Such an arrangement may assist drivers and fleet operators to fulfil their legal obligations, and may also assist fleet operator to make large cost savings by avoiding the replacement of vehicle tyres when it is not required. Such cost savings are provided by the accurate knowledge of tyre tread depths, and in the case of large vehicle fleet operators the operational cost savings may be millions of pounds.

Preferably the body has a flat face for placing against the rolling surface. Such a flat face is tangential to the rolling surface when placed against it, and provides the advantage of further assisting the user to place the measurement device so that the tread depth measurement is substantially along a normal to the rolling surface.

Preferably the measurement device comprises an elongate member for location in the tyre tread, the elongate member being normal to and protruding through the flat face. Such an arrangement is a convenient and reliable way of measuring tread depth.

Preferably the measurement device is operable to record the tread depth upon receiving a record signal from the electronic sensor device that the tread depth measurement is substantially along the normal. Such an arrangement may provide the advantage of automatically recording the tread depth when the required orientation of the measurement deice has been determined.

Preferably the apparatus further includes an alert device operable to provide an alert signal when the measurement device is oriented relative to the rolling surface to provide a tread depth measurement substantially along the normal. Such an alert signal provides the advantage of assisting the user to position the apparatus relative to the rolling surface.

The electronic sensor device may comprise an inductor, a magnetic sensor, a capacitor, a light level detector, a photomicrosensor, or a strain gauge.

In one embodiment the inductor forms an inductor circuit to determine a minimum inductance value, an eddy current loss value, or a Q factor due to the proximity of metal in the tyre for indicating said orientation of the measurement device. Preferably the inductor circuit has an oscillator wherein a frequency of oscillation thereof varies according to the value of the inductor. Preferably the oscillator is a Colpitts oscillator. Such an inductor provides the advantage of a non-contact way of indicating the orientation of the measurement device.

In one embodiment the magnetic sensor forms a magnetic sensor circuit to determine a change in magnetic field due to the proximity of metal in the tyre, the change in magnetic field for indicating said orientation of the measurement device. Such a magnetic sensor provides the advantage of a non-contact way of indicating the orientation of the measurement device.

In one embodiment the capacitor forms a capacitor circuit to determine a maximum capacitance value due to the proximity of rubber of the tyre, the maximum capacitance value for indicating said orientation of the measurement device. Preferably the capacitor circuit has an oscillator wherein a frequency of oscillation thereof varies according to the value of the capacitor. Preferably the oscillator is a Schmitt trigger. Such a capacitor provides the advantage of a non-contact way of indicating the orientation of the measurement device.

In one embodiment the light level detector forms a light level circuit to determine a minimum light level due to the proximity of the tyre, the minimum light level for indicating said orientation of the measurement device. Such a light level detector provides the advantage of a straight forward way of indicating the orientation of the measurement device.

In one embodiment the photomicrosensor is associated with a pin having a leading end protruding through the body for contact with the rolling surface, and a trailing end within the body, the photomicrosensor forming a displacement circuit to determine a distance of the trailing end from the photomicorsensor for indicating said orientation of the measurement device. Preferably the apparatus has a plurality of photomicrosensor associated with respective pins. Preferably the plurality of pins surround the measurement device. Such an arrangement provides the advantage of a straight forward way of indicating the orientation of the measurement device.

In one embodiment the strain gauge forms a deformation circuit to determine a deformation of a part of the body for indicating said orientation of the measurement device. Such an arrangement provides the advantage of a straight forward way of indicating the orientation of the measurement device.

The body may have one or more lights for providing illumination of the tyre tread.

According to a second aspect of the invention there is provided a method of measuring a tyre tread depth using a tread depth measurement apparatus, comprising a body having a measurement device and an electronic sensor device, the method including: determining an orientation of the measurement device relative to a rolling surface of the tyre using the electronic sensor device; and measuring the tread depth using the measurement device when the electronic sensor device has determined that the tread depth measurement is substantially along a normal to the rolling surface.

Such a method provides the advantage that the tread depth can be measured to an improved accuracy, for example up to an accuracy of +/-0.01mm or better. Such an improved accuracy is provided by the electronic sensor device which is able to assist with positioning the body so that the measurement device is measuring along the normal to the rolling surface. The Applicant has discovered that non-normality of the measurement device is an important source of inaccuracy, and may occur when the body is not in full and close contact with the rolling surface of the tyre. Such a method may assist drivers and fleet operators to fulfil their legal obligations, and may also assist fleet operator to make large cost savings by avoiding the replacement of vehicle tyres when it is not required. Such cost savings are provided by the accurate knowledge of tyre tread depths, and in the case of large vehicle fleet operators the operational cost savings may be millions of pounds.

Preferably the body has a flat face, the method including placing the flat face against the rolling surface when measuring the tread depth. With such an arrangement the flat face is tangential to the rolling surface when placed against it, and the method provides the advantage of further assisting the user to place the measurement device so that the tread depth measurement is substantially along a normal to the rolling surface.

Preferably the method further includes providing a record signal using the electronic sensor device when the measurement device is measuring substantially along the normal, and recording the tread depth. Such an arrangement may provide the advantage of automatically recording the tread depth when the required orientation of the measurement deice has been determined.

Preferably the method further includes providing an alert signal when the measurement device is measuring substantially along the normal. Such an alert signal provides the advantage of assisting the user to position the apparatus relative to the rolling surface.

The method may further includ using an inductor, a magnetic sensor, a capacitor, a light level detector, a photomicrosensor, or a strain gauge for the electronic sensor device.

In one embodiment the method further includes determining a minimum inductance value, an eddy current loss value, or a Q factor caused by the proximity of metal in the tyre for indicating said orientation of the measurement device. Such a method provides the advantage of a non-contact way of indicating the orientation of the measurement device.

In one embodiment the method further includes determining a change in magnetic field due to the proximity of metal in the tyre for indicating said orientation of the measurement device. Such a method provides the advantage of a non-contact way of indicating the orientation of the measurement device.

In one embodiment the method further includes determining a maximum capacitance value due to the proximity of rubber of the tyre for indicating said orientation of the measurement device. Such a method provides the advantage of a non-contact way of indicating the orientation of the measurement device.

In one embodiment the method further includes determining a minimum light level due to the proximity of the tyre for indicating said orientation of the measurement device. Such a method provides the advantage of a straight forward way of indicating the orientation of the measurement device.

In one embodiment the photomicrosensor is associated with a pin having a leading end protruding through the body and a trailing end within the body, the method further including placing the leading end on the rolling surface, and determining a distance of the trailing end from the photomicrosensor for indicating said orientation of the measurement device. Such an arrangement provides the advantage of a straight forward way of indicating the orientation of the measurement device.

In one embodiment the method further includes determining a deformation of a part of the body for indicating said orientation of the measurement device. Such an arrangement provides the advantage of a straight forward way of indicating the orientation of the measurement device.

According to an alternative characterisation of the invention there is provided a tread depth measurement apparatus, comprising a measurement device for measuring a tread depth of a tyre tread, and an electronic sensor device for determining when the measurement device is substantially normal to the tyre tread, wherein the apparatus is operable for recording the tread depth upon receiving a signal from the electronic sensor device that the measurement device is substantially normal to the tyre tread.

According to an alternative characterisation of the invention there is provided a tread depth measurement apparatus, comprising a measurement device for measuring a tread depth of a tyre tread, and an electronic sensor device for determining that the measurement device is operable to measure the tread depth substantially along normal to the tyre tread, wherein the apparatus is operable for measuring said tread depth upon receiving a signal from the electronic sensor device that the measurement device is operable to measure the tread depth substantially along said normal.

According to an alternative characterisation of the invention there is provided a method of measuring a tyre tread depth using a measurement device and an electronic sensor device, the method including: determining an orientation of the measurement device relative to the tyre tread using the electronic sensor device; and measuring the tread depth substantially along a normal to the tyre tread.

According to an alternative characterisation of the invention there is provided a method of measuring a tyre tread depth including: using a measurement device to measure the tread depth; and using an electronic sensor device to determine an orientation of the measurement device relative to a rolling surface of the tyre in order to measure the tread depth substantially along a normal to the rolling surface.

Any preferred or optional features of one aspect or characterisation of the invention may be a preferred or optional feature of other aspects or characterisations of the invention.

Brief Description of the Drawings

Other features of the invention will be apparent from the following description of preferred embodiments shown by way of example only with reference to the accompanying drawings, in which;

Figure la & lb show schematic side views of a tyre tread depth measurement apparatus according to an embodiment of the invention;

Figure 2 shows a perspective view of the tyre tread depth measurement apparatus shown in Figure 1;

Figure 3 shows a perspective view of the tyre tread depth measurement apparatus in use;

Figure 4 shows a schematic view of an inductor circuit according to an embodiment of the invention;

Figure 5 shows a schematic view of an inductor circuit according to another embodiment of the invention;

Figure 6 shows a schematic view of a capacitor circuit according to an embodiment of the invention;

Figure 7 shows a schematic view of a capacitor circuit according to another embodiment of the invention;

Figure 8 shows a perspective view of the tyre tread depth measurement apparatus according to another embodiment;

Figure 9 shows a schematic cross section of a pin shown in Figure 8;

Figure 10 shows a graph of relative light current against distance; and

Figure 11 shows steps of a method according to an embodiment of the invention.

Detailed Description

Figures la and lb show schematic side views of a tyre tread depth measurement apparatus according to an embodiment of the invention, generally designated 10. The apparatus 10 has an elongate body 12, which is held in a user’s hand. The body 12 has a head 14 at an end thereof, which has a flat face 16 for placing against a rolling surface 18 of a vehicle tyre 20. In Figure la and lb the vehicle tyre 20 is shown such that the rolling surface 18 represents a width of the vehicle tyre 20 having side walls 19, and so that the elongate body 12 is parallel to a rotational axis (not shown) of the vehicle tyre 20. A tyre tread 21 of the tyre 20 runs circumferentially around the vehicle tyre 20 and into the plane of the drawings.

The head 14 of the apparatus 10 has an elongate member or pin 22 that protrudes through a centre of the flat face 16 such that it is substantially normal to the flat face 16. The pin 22 is also perpendicular to the elongate body 12. The pin 22 is linearly movable relative to the flat face 16 along an axis 24, as shown by arrow 26. The axis 24 is normal to the flat face 16. The pin 22 is biased in a deployed position as shown in Figure la with a spring and linear potentiometer arrangement (not shown) within the head 14. The pin 22 and linear potentiometer comprise a measurement device for measuring pin 22 displacement for measuring a depth of the tyre tread 21.

The head 14 of the apparatus 10 also has an electronic sensor device 28 adjacent to the flat face 16, which is coupled to a sensor circuit 30 of the apparatus 10. The sensor circuit 30 is coupled to an alert device 32 of the apparatus 10, which may be a lamp or an audio device to issue a visible alert or an audible alert to the user. Alternatively the alert device 32 may be a haptic device to provide a haptic alert, e.g. a vibration alert, to the user. Whereas the separate electronic sensor device 28 and the sensor circuit 30 are shown, in some embodiments the electronic sensor device 28 comprises the sensor circuit 30.

In one embodiment the electronic sensor 28 comprises one or more inductors, i.e. coils of wire. Such inductors are operable to interact with a steel band 34 or steel wires embedded within the vehicle tyre 20. Typically a vehicle tyre 20 has such a steel band 34 or steel wires to provide reinforcement thereto. The coils of wire are a plurality of turns of wire that may be arranged in a ring shape so that one side of the ring is parallel to the flat face 16. Alternatively the turns of wire may be arranged as an elongate inductor such that one side thereof is parallel to the flat face 16.

In another embodiment the electronic sensor 28 comprises one or more capacitors. Such capacitors are operable to interact with the rubber of the vehicle tyre 20. The rubbed is a dielectric and increases the capacitance of the capacitor because rubber has a higher dielectric constant (approximately 3.5) compared to free air (approximately 1).

In another embodiment the electronic sensor 28 is a light level detector such as one or more photodiodes. Such a light level detector records a minimum ambient light level when the flat face 16 is in close proximity of the vehicle tyre 20. It will be appreciated that the light level detector is arranged so that it is parallel or normal to the flat face 16. When using the light level detector for the electronic sensor 28 the sensor circuit 30 is a light level circuit that determines a minimum light value when the flat face 16 is against the rolling surface 18, and when the axis 24 is normal to the vehicle tyre 20.

Figures la and lb respectively show the tyre tread depth measurement apparatus 10 prior to, and during, measurement of the tread depth of the tyre 20. In Figure lb like features to the arrangements of Figure la are shown with like reference numerals. As shown in Figure lb the user places the apparatus 10 so that the flat surface 16 is on the rolling surface 18 of the vehicle tyre 20, and so that the pin 22 is within the tyre tread 21 to displace the pin 22. The user then activates the apparatus 10, e.g. by pressing a button (not shown), and the sensor circuit 30 starts to determine whether the flat face 16 is tangential relative to the tyre 20, i.e. so that the axis 24 is along a radius 40 (shown in Figure 3) of the tyre 20. The user may then make minor position adjustments of the apparatus 10 to orient it relative to the tyre 20. The sensor circuit 30 may provide an alert signal to the alert device 32 to activate it so that the user is made aware that the flat face 16 is sufficiently tangential to the tyre 20. When the sensor circuit 30 has determined that the flat face 16 is sufficiently tangential the measurement device records a tread depth 33, in a memory 35. The measurement device may record the tread depth 33 in the memory 35 or on a display screen (not shown) upon receipt of a record signal from the sensor circuit. Such recording may be automatic up receipt of the record signal. The alert device 32 may then indicate to the user that tread depth measurement has been successfully recorded. It will be understood that the tread depth 33 is the distance between the end of the pin 22 and the flat face 16. The alert device 32 may be provided on a separate computer device (not shown) having a processor (not shown). The computer device may further be used to analyse the tread depth measurements. It will be appreciated that the apparatus 10 is a portable tool that may have its own power source, and may be in communication with the separate computer device via a wired or wireless connection.

Figure 2 shows a perspective view of the tyre tread depth measurement apparatus 10 shown in Figure 1. In Figure 2 like features to the arrangements of Figure 1 are shown with like reference numerals. In Figure 2 the orientation of the electronic sensor device 28 is shown in dashed outline. Also shown are four lights 36 which may be provided in some embodiments. The lights 36 may help the user to see so that they can locate the end of the pin 22 into the tyre tread 21 so that it touches a bottom surface thereof. Also shown in Figure 2 is that the head 14 has a relatively small head dimension 38, which is useful so that the head 14 can fit between a wheel arch of a vehicle and the tyre 20.

In the embodiment where the electronic sensor 28 is a light level detector, the lights 36 may be used to provide a more uniform light level to provide a more accurate low light level reading for determining when the axis 24 is sufficiently normal to the tyre tread 21, i.e. along a radius of the tyre 20. Such an arrangement allows the user to minimise the average distance between the flat face 16 and the rolling surface 18 of the tyre 20 by detecting the change in light received by the one or more light level detectors. Alternatively the light level detector may operate using ambient light without the lights 36

Figure 3 shows a perspective view of the tyre tread depth measurement apparatus 10 in use. In Figure 3 like features to the arrangements of Figures 1 and 2 are shown with like reference numerals. In Figure 3 a radius line 40 of the tyre 20 is shown, which meets the rolling surface 18 at a tangent 42 thereof. It will be appreciated that the radius line 40 is a normal to the rolling surface 18. Also shown is an axis 44, which is across the rolling surface 18 and parallel with a rotational axis of the tyre 20. Together the tangent 42 and the axis 44 define a plane such that the radius line 40 is normal to the plane, i.e. normal to the rolling surface 18 of the tyre 20. The embodiments described herein aim to assist the user when positioning the apparatus 10 so that the pin 22 is substantially along the radius line 40, i.e. normal to the rolling surface 18, when a tread depth measurement is taken. When the pin 22 is aligned with the radius line 40 it will be appreciated that the flat surface 16 of the apparatus 10 is in the plane defined by the tangent 42 and the axis 44.

The tyre tread 21 may wear unevenly such that one portion of the circumference may be more worn than another portion, which may be caused by poor steering alignment and/or suspension problems. When such uneven tyre wear occurs the axis 44 may not be parallel to the axis of rotation of the tyre 20. The apparatus 10 may operate to take account of such uneven wear by permitting measurement of the tread depth when the axis 44 is substantially parallel to the axis of rotation of the tyre 20, i.e. when the pin 22 is substantially on the radius line 40. In this context the term substantially parallel means within one or two degree of being parallel. Furthermore, the term substantially on the radius line 40, i.e. normal to the rolling surface 18, means within one or two degree of being on the radius line 40.

Figure 4 shows a schematic view of an inductor circuit 46 according to an embodiment of the invention. The inductor circuit 46 is for use with the one or more inductors for the electronic sensor 28 as mentioned above, such that the sensor circuit 30 and the electronic sensor 28 is the inductor circuit 46. In Figure 4 the inductor circuit 46 has an inductor 48 which may be an air-wound coil. The inductor 48 is connected in parallel with two capacitors 50, 52 to form part of a self-oscillating Colpitts oscillator whereby the frequency of oscillation is changes according to the value of the inductor 48 and the two capacitors 50, 52. The frequency of oscillation of the Colpitts oscillator varies according to the proximity of the steel band 34 or steel wires of the tyre 20, and is measured by an appropriate frequency measuring circuit 54, or using a timer of a suitable microcontroller (not shown). The frequency of oscillation of the Colpitts oscillator is required to be relatively low because the steel band 34 has an effect on the frequency in the kilohertz region. In effect the inductor circuit 46 determines a minimum inductance value of the inductor 48 when the flat face 16 of the apparatus 10 is against the rolling surface 18, and when the pin 22 is in line with the radius line 40, i.e. in other words the pin is normal to the steel band 34.

Figure 5 shows a schematic view of an inductor circuit 56 according to another embodiment of the invention. In Figure 5 like features to the arrangements of Figure 4 are shown with like reference numerals. In Figure 5 the inductor circuit 56 shows the inductor 48 and an integrated circuit 58. The integrated circuit 58 (available from Texas Instrument) is an integrated inductance to frequency converter, and a frequency counter. The integrated circuit 58 also provides a way of measuring the circuit power consumption using the device 60, which is a reference oscillator used for measuring the frequency of oscillation. The integrated circuit 58 is connected to a microcontroller (not shown) using an I2C bus, which simplifies the arrangement of the electronic sensor 28 and sensor circuit 30. It will be appreciated that the steel band 34 or steel wires embedded within the vehicle tyre 20 increases the eddy current losses, and using the integrated circuit 58 such eddy current losses can be measured. Alternatively the sensor circuit 30 may be used to determine a change in a related parameter such as a Quality factor, i.e. Q factor, caused by the proximity of the steel band 34 of the tyre 20.

In an alternative arrangement to the embodiment of Figures 4 and 5 the electronic sensor 28 comprises one or more magnetic sensors. Such magnetic sensors may be Hall effect sensors or Microelectromechanical systems (MEMS) devices, which are operable to interact with the steel band 34 or steel wires embedded within the vehicle tyre 20. When using the one or more magnetic sensors for the electronic sensor 28 the sensor circuit 30 is operable to determine magnetic field changes due to the presence of the steel band 34 when the flat face 16 is against the rolling surface 18, and when the pin 22 is in line with the radius 40, i.e. in other words the pin 22 is normal to the steel band 34. In this embodiment the sensor circuit 30 may be termed a magnetic sensor circuit.

It will be appreciated that depending on whether the electronic sensor 28 comprises an inductive or magnetic sensor, the steel band 34 in the tyre 20 may increase the eddy current losses, or change the inductance of the electronic sensor 28, or change the magnetic field at the electronic sensor 28. In effect the inductive or magnetic sensor the effected by the steel band 34 or steel wires embedded within the vehicle tyre 20.

Figure 6 shows a schematic view of a capacitor circuit 62 according to an embodiment of the invention. The capacitor circuit 62 is for use with the one or more capacitor for the electronic sensor 28 as mentioned above, such that the sensor circuit 30 and the electronic sensor 28 is the capacitor circuit 62. In Figure 6 the capacitor circuit 62 has a plurality of capacitor plates 64 that are separated such that proximity of the vehicle tyre 20 changes the measured capacitance. Each capacitor plate 64 is a metal plate that may be on a printed circuit board, and may be in contact with the rolling surface 18 of the tyre 20 when a tread depth measurement is being taken. Alternatively, each capacitor plate 64 may be embedded within the plastic that comprises the flat face 16. It will be appreciated that each capacitor plate 64 is arranged so that it is parallel to the flat face 16 of the apparatus 10. Whereas only three capacitor plates 64 are shown there may be many more in the apparatus 10.

Each capacitor plate 64 is connected to a respective CMOS Schmitt trigger inverter 66. Each Schmitt trigger inverter 66 has a respective feedback resistor 68. Together each capacitor plate 64, Schmitt trigger inverter 66 and resistor 68 form respective Schmitt triggers. Each Schmitt trigger forms an oscillator whereby the frequency of oscillation changes according to the value of at the capacitor plates 64. The frequency of oscillation of the Schmitt triggers varies according to the proximity of the tyre 20, and is measured by an appropriate frequency measuring circuit 70, or using a timer of a suitable microcontroller (not shown). As the tyre 20 approaches the flat face 16, the measured capacitance increases due to the increased dielectric constant of rubber which causes the frequency to reduce. In effect the capacitor circuit 62 determines a maximum capacitance value at the capacitor plates 64 when the flat face 16 of the apparatus 10 is against the rolling surface 18, and when the pin 22 is in line with the radius line 40.

Figure 7 shows a schematic view of a capacitor circuit 72 according to another embodiment of the invention. In Figure 7 like features to the arrangements of Figure 6 are shown with like reference numerals. In Figure 7 the capacitor circuit 72 shows the capacitor plate 64 and an integrated circuit 74. The integrated circuit 74 (available from Texas Instrument) is an integrated capacitance to frequency converter. The integrated circuit 72 is connected to a microcontroller (not shown) using an I2C bus, which simplifies the arrangement, which simplifies the arrangement of the electronic sensor 28 and sensor circuit 30. The integrated circuit 74 also has a shield connection (SHFD1) which is connected to a plate 76 or PCB layer to reduce interference from mains power and other potential noise sources.

Figure 8 shows a perspective view of the tyre tread depth measurement apparatus according to another embodiment. In Figure 8 like features to the arrangements of Figure 2 are shown with like reference numerals. In Figure 8 the electronic sensor 28 is coupled to a plurality of pins 80 that protrude from the flat face 16. In Figure 8 there are eight pins 80 shown around a perimeter of the flat face 16. Each pin 80 is linearly movable into and out of the flat face 16 as shown by arrow 81 such that the direction of linear travel of each pin 80 is normal to the flat face 16. Each pin 80 is biased in a deployed position as shown in Figure 8 with a respective spring 82 (See Figure 9).

Figure 9 shows a schematic cross section of a pin 80 shown in Figure 8. In Figure 9 like features to the arrangements of Figure 8 are shown with like reference numerals. In Figure 9 the pin 80 is shown to protrude through the flat face 16 by about 2mm. Also shown is the spring 82, and an Infra-Red (IR) reflective transceiver 84 or photomicrosensor that is mounted on a printed circuit board 86 within the head 14 of the apparatus 10. Infra-Red (IR) reflective transceiver 84 emits IR light and a photo detector that detect reflected IR light. The reflective transceiver 84 is operable to sense the proximity of a rear surface 85 or trailing end of the pin 80, and is operable to provide a current measurement over the range 1 to 3mm as shown in Figure 10. It will be appreciated that each pin 80 has a respective reflective transceiver 84 such that the plurality of reflective transceivers 84 comprise part of the sensor circuit 30.

Figure 10 shows a graph of relative light current 88 against distance 90. The relative light current 88 is produced by the reflective transceiver 84 shown in Figure 9, and the distance 90 is between the rear surface 85 and the reflective transceiver 84. The relative light current 88 is measured as a percentage, and the distance 90 is measured in mm. In effect the reflective transceiver 84 can determine a distance of each rear surface 85 to its respective reflective transceiver 84. The sensor circuit 30 collects the distance data from all eight pins 80 when the leading end of each pin 80 is urged against the rolling surface 18 to determine when the flat face 16 is within the plane defined by the tangent 42 and the axis 44. The sensor circuit 30 may be termed a displacement circuit. Such an arrangement measures pin displacement across the electronic sensor 28 when the flat face 16 is against the rolling surface 18 of the vehicle tyre 20 to determine how well the flat face 16 is in contact with the rolling surface 18.

In operation the pins 80 of the embodiment described in Figures 8-10 assist the user when positioning the apparatus 10 so that the elongate member 22 is substantially along the radius line 40, i.e. normal to the rolling surface 18, when a tread depth measurement is taken. In effect the plurality of pins 80 allow the user to minimise the average distance between the flat face 16 and the rolling surface 18 of the tyre 20.

It will be appreciated that in alternative embodiments two, four or six pins 80 may be used instead of eight pins 80. However, eight pins 80 provide the advantage of a more reliable way of ensuring that the elongate member 22 is able to measure the tread depth for the various different tyre tread patterns that may be encountered by the apparatus 10. For example, with eight pins 80 the majority of the pins 80 contact the rolling surface 18 of the tyre 20, and some of the pins 80 may be within the tyre tread. With such an arrangement the sensor circuit 30 may ignore the distance reading from pins 80 within the tyre tread.

In an alternative embodiment the electronic sensor device 28 comprises one or more strain gauges or similar devices, whereby the strain gauges are attached behind the flat face 16 and inside the head 14. With such an arrangement when the flat face 16 is in contact with the rolling surface 18 the pressure of the tyre surface against the flat face 16 causes a slight deformation thereof which is recorded by the strain gauges and the sensor circuit 30. The sensor circuit 30 then determines the amount and pattern of the deformation to determine whether the flat face 16 is tangential relative to the tyre 20, i.e. so that the axis 24 is along a radius 40. The sensor circuit 30 may alternatively be termed a deformation circuit. In effect the strain gauges allow the user to minimise the average distance between the flat face 16 and the rolling surface 18 of the tyre 20 by detecting the change in deformation of the flat face 16 by detecting the pressure of the rolling surface 18 on the flat face 16.

Figure 11 shows steps of a method according to an embodiment of the invention, generally designated 100. It will be appreciated that the steps may be performed in a different order, and may not necessarily be performed in the order shown in Figure 11. The method 100 is a way of measuring a tyre tread depth using a tread depth measurement apparatus 10, comprising a body 12 having a measurement device and an electronic sensor device 28. The method includes determining an orientation of the measurement device relative to a rolling surface 18 of the tyre 20 using the electronic sensor device 28, and measuring the tread depth using the measurement device when the electronic sensor device 28 has determined that the tread depth measurement is substantially along a normal to the rolling surface 18, as shown at 102.

The body 12 has a flat face 16, and the method includes placing the flat face 16 against the rolling surface 18 when measuring the tread depth, as shown at 104. The method further includes providing a record signal using the electronic sensor device 28 when the measurement device is measuring substantially along the normal 40, and recording the tread depth, as shown at 106. The method further includes providing an alert signal when the measurement device is measuring substantially along the normal 40, as shown at 108.

The method further includes using an inductor 48, a magnetic sensor, a capacitor 64, a light level detector, a photomicrosensor 84, or a strain gauge for the electronic sensor device 28, as shown at 110. The method further includes determining a value from the electronic sensor device 28 for indicating said orientation, as shown at 112. The method further includes determining a minimum inductance value, an eddy current loss value, or a Q factor caused by the proximity of metal 34 in the tyre 20 for indicating said orientation of the measurement device, as shown at 112. The method further includes determining a change in magnetic field due to the proximity of metal 34 in the tyre 20 for indicating said orientation of the measurement device, as shown at 112. The method further including determining a maximum capacitance value due to the proximity of rubber of the tyre 20 for indicating said orientation of the measurement device, as shown at 112. The method further including determining a minimum light level due to the proximity of the tyre for indicating said orientation of the measurement device, as shown at 112. The method further includes determining a deformation of a part of the body 12 for indicating said orientation of the measurement device, as shown at 112.

The photomicrosensor 84 is associated with a pin 80 having a leading end protruding through the body 12 and a trailing end 85 within the body 12, the method further including placing the leading end on the rolling surface 18, and determining a distance of the trailing end 85 from the photomicrosensor 84 for indicating said orientation of the measurement device, as shown at 112.

An important factor in the sales process is that customers tend to accept recommendations to change their tyres when the information about tyre wear is presented in a computerised format. This means that if the customer can be shown a computer generated report, either on paper or on a screen, they are more likely to replace their tyres. In addition, if the wear pattern is uneven, it may indicate that there is a problem with steering geometry which may need to be corrected. When this data is presented verbally by the technician, it does not have the authority associated with electronic measurement and displayed on a computer device. Accordingly the embodiments herein may assist garages in selling tyres.

Whereas the above embodiments described the measurement device comprising the pin 22 and linear potentiometer, alternatively the measurement device may be any device for measuring the depth of tyre tread 21 such as a laser device. With such an alternative measurement device the electronic sensor device 28 determines that the measurement device is sufficiently tangential with the rolling surface 18 of the tyre 20, or assists with determining that the measurement of the tread depth is performed along the radius line 40, i.e. normal to the rolling surface 18.

It will be understood from the above embodiments that whereas the flat surface 16 assists the user to keep the pin 22 along the radius 40, the electronic sensor 28 provides a more accurate way of doing so. The Applicant has realised that it is difficult for the user to be sure that the pin 22 is along the radius 40 (i.e. normal to the rolling surface 18), which introduces an important source of inaccuracy. The embodiments herein help with such alignment of the pin 22 with the radius 40 in order to minimise the average distance between the flat face 16 and the rolling surface 18 of the tyre 20. Such an apparatus provides the advantage that the tread depth can be measured to greater accuracy, for example up to an accuracy of +/-0.01mm or better.

Claims

1. A tread depth measurement apparatus for measuring a tread depth of a tyre, comprising a body having a measurement device for measuring the tread depth, wherein the body further includes an electronic sensor device to determine an orientation of the measurement device relative to a rolling surface of the tyre to provide the tread depth measurement substantially along a normal to the rolling surface.

2. An apparatus according to claim 1, wherein the body has a flat face for placing against the rolling surface.

3. An apparatus according to claim 2, wherein the measurement device comprises an elongate member for location in the tyre tread, the elongate member being normal to and protmding through the flat face.

4. An apparatus according to claim 1, 2 or 3, wherein the measurement device is operable to record the tread depth upon receiving a record signal from the electronic sensor device that the tread depth measurement is substantially along the normal.

5. An apparatus according to any preceding claim, and further including an alert device operable to provide an alert signal when the measurement device is oriented relative to the rolling surface to provide a tread depth measurement substantially along the normal.

6. An apparatus according to any preceding claim, wherein the electronic sensor device comprises an inductor, a magnetic sensor, a capacitor, a light level detector, a photomicrosensor, or a strain gauge.

7. An apparatus according to claim 6, wherein the inductor forms an inductor circuit to determine a minimum inductance value, an eddy current loss value, or a Q factor due to the proximity of metal in the tyre for indicating said orientation of the measurement device.

8. An apparatus according to claim 7, wherein the inductor circuit has an oscillator wherein a frequency of oscillation thereof varies according to the value of the inductor.

9. An apparatus according to claim 6, wherein the magnetic sensor forms a magnetic sensor circuit to determine a change in magnetic field due to the proximity of metal in the tyre, the change in magnetic field for indicating said orientation of the measurement device.

10. An apparatus according to claim 6, wherein the capacitor forms a capacitor circuit to determine a maximum capacitance value due to the proximity of rubber of the tyre, the maximum capacitance value for indicating said orientation of the measurement device.

11. An apparatus according to claim 10, wherein the capacitor circuit has an oscillator wherein a frequency of oscillation thereof varies according to the value of the capacitor.

12. An apparatus according to claim 6, wherein the light level detector forms a light level circuit to determine a minimum light level due to the proximity of the tyre, the minimum light level for indicating said orientation of the measurement device.

13. An apparatus according to claim 6, wherein the photomicrosensor is associated with a pin having a leading end protruding through the body for contact with the rolling surface, and a trailing end within the body, the photomicrosensor forming a displacement circuit to determine a distance of the trailing end from the photomicorsensor for indicating said orientation of the measurement device.

14. An apparatus according to claim 13, and further including a plurality of photomicrosensor associated with respective pins.

15. An apparatus according to claim 14, wherein the plurality of pins surround the measurement device.

16. An apparatus according to claim 6, wherein the strain gauge forms a deformation circuit to determine a deformation of a part of the body for indicating said orientation of the measurement device.

17. An apparatus according to any preceding claim, wherein the body has one or more lights for providing illumination of the tyre tread.

18. An apparatus as substantially described herein with reference to Figures 1-10 of the accompanying drawings.

19. A method of measuring a tyre tread depth using a tread depth measurement apparatus, comprising a body having a measurement device and an electronic sensor device, the method including: determining an orientation of the measurement device relative to a rolling surface of the tyre using the electronic sensor device; and measuring the tread depth using the measurement device when the electronic sensor device has determined that the tread depth measurement is substantially along a normal to the rolling surface.

20. A method according to claim 19, wherein the body has a flat face, the method including placing the flat face against the rolling surface when measuring the tread depth.

21. A method according to claim 19 or 20, and further including providing a record signal using the electronic sensor device when the measurement device is measuring substantially along the normal, and recording the tread depth.

22. A method according to claim 19, 20 or 21, and further including providing an alert signal when the measurement device is measuring substantially along the normal.

23. A method according to any of claims 19 - 22, and further including using an inductor, a magnetic sensor, a capacitor, a light level detector, a photomicrosensor, or a strain gauge for the electronic sensor device.

24. A method according to claim 23, and further including determining a minimum inductance value, an eddy current loss value, or a Q factor caused by the proximity of metal in the tyre for indicating said orientation of the measurement device.

25. A method according to claim 23, and further including determining a change in magnetic field due to the proximity of metal in the tyre for indicating said orientation of the measurement device.

26. A method according to claim 23, and further including determining a maximum capacitance value due to the proximity of rubber of the tyre for indicating said orientation of the measurement device.

27. A method according to claim 23, and further including determining a minimum light level due to the proximity of the tyre for indicating said orientation of the measurement device.

28. A method according to claim 23, wherein the photomicrosensor is associated with a pin having a leading end protruding through the body and a trailing end within the body, the method further including placing the leading end on the rolling surface, and determining a distance of the trailing end from the photomicrosensor for indicating said orientation of the measurement device.

29. A method according to claim 23, and further including determining a deformation of a part of the body for indicating said orientation of the measurement device.

30. A method as substantially described herein with reference to Figure 11 of the accompanying drawings.