GB2490302A

GB2490302A - TYre pressure warning system

Info

Publication number: GB2490302A
Application number: GB1104095.3A
Authority: GB
Inventors: Andy Bradbury; Nick Barnett
Original assignee: SAFETVALVE Ltd
Current assignee: SAFETVALVE Ltd
Priority date: 2011-03-10
Filing date: 2011-03-10
Publication date: 2012-10-31
Also published as: GB201104095D0

Abstract

Under inflation is a common cause of catastrophic failure of pneumatic tyres. Consequently, efforts have been made to provide means to warn a driver when a tyre is under inflated. One approach is to use a pressure measuring device mounted onto an external threat of the vale stem. A problem with this is that there is a risk of it being blown off the stem by the air pressure within the tyre. Other systems include a sensor mounted within the tyre cavity which comprises a transmitter which transmits pressure information to a receiver within the cabin of the car. This overcomes the problems of the other solution but is expensive to implement. These problems are overcome by integrating the alert device with a tyre valve stem, which is usually formed as a separate piece to the tyre. The sensor can be mounted within the tyre cavity, and an alert means, such as a light, can be mounted to the portion of the stem lying outside of the tyre where it can be seen by the vehicle's owner.

Description

Tyre Pressure Warning Device Under inflation is a common cause of the catastrophic failure of tyres and leads to a significant number of road casualties each year.

In efforts to mitigate this problem, certain territories are putting, or have put into effect, legislation which requires new vehicles to be provided with means to warn a driver when a tyre is under-inflated.

Various systems to provide this type of alert have been proposed. One approach, as exemplified in US2005062592, comprises a pressure measuring device adapted to be mounted onto the external thread of the valve stem. When installed, the device depresses the poppet of the valve stem so that the pressure sensor is exposed to the pressure within the tyre. The device comprises an indicator, such as a light, which illuminates when the air pressure within the tyre drops below a predetermined threshold.

This arrangement suffers from a number of problems. For example, because the device holds the valve open, it is necessary for the device to provide the seal to prevent the tyre deflating. The pressure within the tyre inherently acts to press the device off the valve stem. This bias, particularly in combination with other forces experienced when the vehicle is in motion, causes the device to loosen until it no longer acts upon the valve. The device can eventually loosen sufficiently that it falls off. It is possible, in certain circumstances, when the air pressure within the tyres rises sufficiently high, that the device can be violently ejected from the valve stem.

A further problem is that the device can be easily unscrewed from the valve stem and stolen. To combat this, some devices are provided with locking sleeves and keys.

This inconveniences the owner, who must retain the key and unlock the device each time the tyre needs inflating.

An alternative system comprises a pressure sensor which incorporates a valve stem.

The pressure sensor is mounted within the tyre cavity and comprises a transmitter for transmitting data from the sensor to a receiver within the cabin of the vehicle.

Examples of such systems are sold under the name TyresureTM.

This arrangement overcomes a number of the problems of valve stem mounted devices. It cannot be stolen easily as it is retained by the rim of the wheel. It also circumvents the problem of the monitor being forced off the valve stem by the pressure within the tyre. Nevertheless, this arrangement is not ideal. For example, it is relatively expensive to produce because it requires a separate receiver. Wireless transmitters consume a relatively large amount of power which reduces the lifetime of the battery within the monitor. Cars which are not manufactured with the receiver integrated into the dashboard, will typically require a stand alone unit, which clutters the cabin of the vehicle. Non-integrated units will probably need to be powered through the ear's power connector (cigarette lighter receptacle), which may already be used for phone chargers, satellite navigation devices and other electronic equipment.

An objective of the present invention is to provide an improved system which is cheap to manufacture, easy to be installed, and which overcomes or at least

meliorates the problems of the prior art.

According to the invention there is provided apparatus for sensing the pressure within a pneumatic tyre and for providing an alert when the pressure falls below a safe level, the device having a sensor arranged, when the device is installed, to reside within a tyre cavity formed between the tyre and a wheel and to provide an output indicative of the sensed pressure within the tyre cavity; means effective to receive the output of the sensor and to activate an alerting device when the received output indicates that the pressure within the tyre is below a safe level; wherein the alerting device, when the apparatus is in use, is coupled to the wheel outside of the tyrc cavity.

In a preferred embodiment the apparatus comprises an electrical connection, typically a wire, which when the apparatus is in use, passes through a valve hole in the wheel.

This precludes the need for relatively power hungry and expensive wireless transmitters, and allows as much of the apparatus as possible to be housed within the relatively safe environment of the tyre cavity.

Preferably the electrical connection exists between the alerting device and the means effective to activate the alerting device when the pressure within the tyre is determined to be below a safe level. The alerting device, which is preferably a light source such as one or more LCDs can be easily identified by a driver when approaching or moving around the vehicle.

It is preferred that the apparatus take the form of a unit which incorporates the valve stem used to inflate and deflate the tyre. As such, it can have an elongate portion which houses the valve and the light source, and is adapted to protrude through the valve hole of the wheel outside of the tyre cavity so as to provide connection to a pump. Positioning the light source outside of the tyre cavity means it can be viewed by a driver walking around the vehicle.

An inner portion of the unit, when installed, sits within the tyre cavity and comprises the pressure sensor and a seal to provide an air tight seal around the valve hole. In this way, the unit can be used as a replacement for traditional valve stems and be installed, e.g. by a tyre fitter, in an identical way. In order that air can be pumped into the tyre, the unit preferably defines a channel which extends through the body of the unit. Air flow through the channel is controlled by the valve.

As is common with traditional valve stems, it is anticipated that the housing of the valve will be embedded within a moulding which is preferably made from an elastomeric material such as a synthetic rubber. This provides shock protection, an air tight seal around the valve hole, and an interference fit with valve hole to retain the unit in position. It is also preferred that the light source be embedded (fully or otherwise) into the moulding. Tn order that the light from the light source can be seen through the moulding material, it is preferred that the moulding material be transparent, translucent or otherwise see-through in at least the portion of the unit into which the light source is mounted.

The means effective to receive the output of the sensor and effective to activate the alerting device when the pressure within the lyre is determined to be below a perceived safe level, will probably comprise circuitry which may be embedded into the moulding, preferably within the portion housed within the tyre cavity. This allows the circuitry to be made larger and so less expensively. Positioned inside the cavity, the circuitry is protected from outside elements.

The electrical connection, which is also preferably embedded into the moulding, may extend from the circuitry inside the tyre cavity, along the elongate portion, to the light source. The light source may comprises multiple lights positioned around a valve housing of the valve.

Alternatively, in another embodiment, the light source may be located within the tyre cavity, and the apparatus comprises means to guide the light, e.g. an optical fibre, to a projecting means outside of the tyre cavity. Preferably the projecting means would comprise a light-guide collar located around a valve housing in order to project the light simultaneously through an angle greater than 180°, and more preferably substantially 360°.

It is preferred that the apparatus has means to self-calibrate the safe pressure level upon inflating the tyre. This allows the device to be installed into almost any wheel without the need to pre-program the valve with the normal operating pressure for a specific tyre.

This feature is considered to have inventive merit in its own right and, therefore, according to a second aspect of the invention, there is provided a method of calibrating a tyre pressure warning device comprising: taking a pressure reading and comparing the reading with a stored value corresponding to a threshold pressure; if the comparison indicates the pressure is equal or above the threshold pressure, taking a further pressure reading and using this to record a calibrated pressure value for the device.

In one embodiment of the method, the further pressure reading may be taken after a period of time which would generally be thought sufficient for a tyre to be fully inflated, e.g. around 5 minutes. This further reading, or a value derived from this reading could be used as the calibrated pressure value. Alternatively, multiple further reading may be taken until consecutive readings indicate that the pressure has not changed, or has changed within an acceptable amount, whereupon one of the consecutive readings is used to derive the calibrated pressure value.

The invention will now be described by way of example with reference to the following figures in which: Figure 1 is a perspective cutaway of a tyre pressure monitor and alert device installed on a wheel of a vehicle; Figure 2 is an axial cross-section through the monitor and alert device shown in Figure 1; Figure 3 is a block diagram illustrating the functioning of the monitor; Figure 4 is a pressure-time graph illustrating a pressure profile within a tyre over the life time of a tyre; and Figure 5 is a side elevation illustrating an alternative embodiment of the monitor.

Referring first to Figures 1 and 2, there is shown a vehicle wheel assembly having a wheel 1 with a rim 1A, flanges lB and a valve hole 1C (Fig 2). The wheel 1 supports a tyre 2, having a treaded portion 2A and side walls 2B each defining a bead 2C which catches against the inside surfaces of the flanges 1 B to retain the tyre 2 onto the wheel 1. A tyre cavity 3 is defined between the inside surface of the tyre 2 and the wheel rim 1A.

Mounted on the wheel 1 is a tyre pressure sensing and alarm unit 10. The unit 10 comprises a narrow elongate portion 1OA which protrudes through valve hole 1 C (Fig 2), and a relatively wide portion 1 OB which sits within the tyre cavity 3 against the inside of the wheel rim 1A to form an air-tight seal around the valve hole 1C. The unit 10 is retained in position by an interference fit with the valve hole 1C.

The tip 1 OC of the elongate portion 1 OA is moulded from a transparent synthetic plastics material, such as polyurethane (PU) or other thermoplastic elastomer, whilst the remainder of the unit 10 is moulded from conventional opaque material. The relatively narrow, elongate, portion 1OA of the housing incorporates a valve housing 11 containing a valve member and valve seat (not shown). The threaded free end 1 1A of the housing 11 protrudes from the moulded part 1OA to enable engagement with a pump attachment (not shown) for inflation and deflation of the tyre 2. Enveloped within the see-through moulded part bA, are light emitting diodes (LED5) 12A, 12B.

The LEDs 12A, 12B are positioned at substantially diametrically opposite positions outside of the valve housing 11, so that at least one LED 12A, 12B will be clearly visible irrespective of the rotational position of the unit 10 relative the wheel 1.

A PCB 13 is embedding into the portion 1 OB of the unit 10, which in use is contained within the tyre cavity 3. The PCB 13 carries components including a microcontroller 14, memory 15, sensor 16, transmitter 17, antenna 18 (formed from a conductive track) and a battery (button cell) 19, which provide a number of the functions illustrated schematically in Figure 3.

To provide fluid connection between the valve 11 and the tyre cavity 3, the unit 10 defines a channel 1 OD which extends from the valve member 11 through the elongate portion to an outer surface of the moulding.

The moulding 10A also defines a passage 10E extending from the sensor 16 to the outer surface of the moulding pan 1 OB. This allows the moulding to substantially envelope the sensor 16 so as to provide impact protection, whilst still exposing the sensor 16 to the air within the tyre cavity 3.

Electrical connection to the LEDs 12A and 12B is provided by sheathed conductive wires 18 which extend through the moulding 1OA of the narrow portion lOB, and in this way through the valve hole 1C of the wheel 1, to connection with the PCB 13 inside of the tyre cavity 3.

Referring to figure 3, pressure sensor 16 arranged to sense the air pressure within the tyre cavity 3 and to produce a signal indicative thereof an analogue to digital converter 20 to process the signal from the sensor 16, a processor 14A arranged to receive the converted signal, a clock 21 timer 22, a store 15, transmitter 18 and antenna 19. The functions of the processor 14A, ADC 20, clock 21 and timer 22 are performed by a single microcontroller. A suitable such microcontroller is the PlC 16LF 1826. The programming of the processor 14A to provide the following functions will be understood by programmer skilled in the art.

The store 15 is arranged to hold at least values P1, P2 which correspond to an initiation tyre pressure (P 1), and a calibrated tyre pressure (P2). The initiation tyre pressure is set at a value above typical variations in ambient pressure (ISO standard atmospheric pressure is 1013.2milliBar which in the UK fluctuates by up to around 0.6psi), but below that which would be expected in a fully inflated tyre, for example 1 Opsi above ambient. The value for P1 is programmed into the store 15 before the unit 10 is first used. Until the device 10 is first used, the value for P2 is empty.

The unit 10 may optionally be provided with an interface (not shown), e.g. pin connector, to provide means for the manufacturer to set the initiation tyre pressure P1.

Alternatively the store may be pre-programmed with a specific pressure P1, and thus the interface is unnecessary.

Before the unit 10 is used for the first time, it operates in a pre-calibration' mode.

The timer 22 in conjunction with the clock 21 is arranged to wake' the processor 14 at set regular intervals, e.g. every thirty seconds, though a longer or short period may be chosen. Upon receiving said signal from the timer 22, the processor 14 takes a measurement from the sensor 16 and compares this with the value P1 in store 15. If less than P1, the unit 10 will return to sleep so as to conserve power.

If the pressure sensed by the sensor 16 is determined to be greater than P1 then the unit will progress to a calibration mode' to obtain a value for the calibrated tyre pressure P2. This can be performed in several ways.

In one method, the timer is set to cause processor 14 to take a further pressure reading after a set period of time and to record this reading as the value for P2. The interval before taking the further reading is chosen to give sufficient time for the tyre 2 to be inflated to the correct operating pressure. A suitable interval would, for example, be 5 minutes.

In an alternative method, the processor 14 does not record a value for P2 until consecutive readings taken from sensor indicate that the tyre pressure has not changed, or has only changed by a tolerated amount. The first further reading may be taken after 5 minutes, as used in the first method, though a shorter (e.g. 30 seconds) or longer period of time may be chosen instead. The reading is stored in store 15 as P3. The next further reading is then compared by the processor 14 with the value for P3. If the value is not accepted, the value of the next further reading replaces the value of P3 in the store. The process repeats until a value is accepted at which point it is recorded for P2.

Once a calibrated tyre pressure value P2 is obtained, the unit 10 assumes a calibrated' mode. The unit operates in a sleep condition and the clock and timer are arranged to wake' the processor and sensor at regular intervals, e.g. ever thirty seconds. Upon receiving said signal from the timer, the processor 14 takes a measurement from the sensor 16 and compares this with the value P2 in store 15. If equal or more than P2, the unit 10 will return to the sleep condition so as to conserve power.

The processor 14 may use the calibrated value for P2 to derive an acceptable range of pressures within which the sensed tyre pressure can fall or rise without activating the alarm. It may calculate this range, for example, based on a percentage on either or one side of the value P2, e.g. P2 ± 10%. A small or larger percentage may be chosen.

Alternatively, the range could be calculated using a fixed difference on one or both sides, e.g. P2 ± 3psi. Because over inflation is generally less dangerous than under inflation the lower limit of the range may be selected to be near the calibrated pressure and the upper limit of the range. The provision of a range means that the driver is not inconvenienced with warnings for insignificant pressure drops, but will still be alerted before the pressure within the tyre becomes unsafe.

If the pressure is determined to be unacceptably lower than the P2 value, the processor 14 will effect the operation of LEDs 12A, 12B. The LEDs 12A, 12B provide an alert to the driver that the tyre 2 is under inflated and needs attention.

The LEDs 12A, 12B may be programmed to produce a steady light, flashing light, or combination thereof Additionally, they may be programmed to change pattern depending upon the relative pressure of the tyre, e.g. a flashing light when the pressure is a little low, or a flashing light when the pressure is dangerously low. This process would probably require the processor 14 to calculate several acceptable ranges based on P2.

The processor 14 may simultaneously causes a signal to be transmitted via transmitter 18, and antenna 19 to be received by a remote receiver, e.g. placed within the cabin of the vehicle, or on a keyflob. The remote receive may comprise a further alert in the form of light source, siren or display to provide a secondary alert to the driver.

-10 -Figure 4 charts the air pressure within a tyre before inflation, during inflation, during use and deflation. Note: the x-axis does not show time linearly. Some sections show time stretched or compressed in order to more clearly illustrate events.

During period A, the unit 10 is installed into a wheel; e.g. as a replacement to a won standard valve stem during a tyre change. The unit 10 operates in pre-calibration mode' whereby the timer 22 causes a pressure reading to be taken every 30 seconds and compares the reading with P1. Towards the end of period A, inflation of the tyre 2 begins.

During inflation, the pressure within the tyrc 2 increases, and at ti exceeds the value for P1 which in this example is set at 1 Opsi (though a value, for example, between Spsi -25 psi could be used instead). A reading taken by the sensor at time t2, after the tyre has been inflated above P1, is determined to be greater than P1. This prompts the processor 14 to progress to calibration mode', represented by period B. In this example, the processor 14 is programmed to use the first hereinbefore described method wherein a pressure reading taken at time t3, 5 minutes after ti, is used to record a value for P2. Upon recording a value for P2, the processor 14 progresses to a calibrated mode' represented by period C. In calibrated mode' the timer 22 prompts the processor 14 to take an air pressure reading every 30 seconds, and to compare this with an accepted tolerance pressure P2' derived from P2 by the processor 14.

Over time, air slowly escapes from the inflated tyre 2, reducing the air pressure within the tyre cavity 3. At time t4 the pressure falls below the accepted tolerance pressure P2'. Shortly thereafter, at time t5, a pressure reading is determined to be below P2'. This prompts the processor 14 to progress to an alert mode' D in which LEDs 12A, 12B are illuminated in order to provide a waning to the driver. Whilst in the alert mode, tyre pressure readings continue to be taken regularly and compared with P2'. -11 -

Upon noting the illuminated LEDs 12A, 12B, the driver inflates the tyre 2 to its operating pressure P2. The unit continues to take regular pressure readings until a tyre pressure reading taken at t5 is determined to be greater than P2. This prompts the processor 14 to deactivate the LEDs 12A, 12B, and the unit 10 reverts to calibrated mode'.

The far right portion of the chart illustrates a situation where the tyre deflates relatively quickly, either unintentionally, e.g. through a fast puncture, or intentionally, e.g. where the tyre is being replaced. Upon sensing the reduction in pressure, the processor 14 initially activates the alert l2A, 12B. When output readings from the sensor 16 taken from time t6 to t7 indicate that the pressure remains below a threshold pressure, in this case P1, for a period of 2 minutes, the processor 14 places the unit back into pre-calibration mode to re-calibrate the value for P2. In other embodiments a period less or greater than 2 minutes may be used to initiate the reset.

Figure 5 illustrates an alternative embodiment in which a LED 120 is mounted inside the tyre cavity 3 and the unit 10 comprises a light guide collar 120A located around the valve stem outside of the tyre cavity. An optical cable 120B mounted \vithin the moulding, guide light from the light source 120, though the valve hole 1C to the collar 120A which is arranged to project the light simultaneously about a wide angle of directions, preferably at least 180° or more preferably substantially 360°. The moulding material around the light guide collar 150A is transparent/see through in order that light can pass through the moulding. Although figure 5 illustrates the PCB and light source 150 without an enveloping moulding, an enveloping moulding may be provided which may be see through or opaque.

LEDs are used for the light source as they are compact, resilient to impact and operate to produce a relatively bright light at a relatively low power. Nevertheless, other light sources may be used, particularly if the performance of the above characteristics is greater.

-12 -Although the moulding is made from two different materials so as to have opaque and non-opaque portions, it is possible that the whole moulding is manufactured to be non-opaque. It is preferred that the moulding surrounding the LEDs is transparent to maximise the transmission of visible light from the LEDs. Nevertheless non-transparent materials may be used so long as they allow light from the LEDs to be seen through the moulding.

The portion of moulding surrounding the light source may be shaped in such a way to refract or reflect light from the light source, e.g. by means of a locally convex moulding profile or through moulded Fresnel lens elements, so as to provide the alert with improved viewing characteristics.

The interval period of 30 seconds is used to making sensor reading during pre-calibrated, calibrated and alert modes. Nevertheless, the length of this interval may be varied, and may be different for different modes.

Claims

-13 -CLAIMS1. Apparatus for sensing the pressure within a pneumatic tyre and for providing an alert when the pressure falls below a safe level, the device having a sensor arranged, when the device is installed, to reside within a tyre cavity formed between the tyre and a wheel and to provide an output indicative of the sensed pressure within the tyre cavity; means effective to receive the output of the sensor and to activate an alerting device when the received output indicates that the pressure within the tyre is below a safe level; wherein the alerting device, when the apparatus is in use, is coupled to the wheel outside of the tyre cavity.
2. Apparatus according to claim 1 comprising an electrical connection which, when the apparatus is in use, passes through a valve hole in the wheel.
3. Apparatus according to claim 2 wherein the electrical connection exists between the alerting device and the means effective to activate the alerting device when the pressure within the tyre is determined to be below a safe level.
4. Apparatus according to claim 1, 2 or 3 wherein the alerting device comprises a light source.
5. Apparatus according to claim 4 wherein the apparatus comprises a device having a channel therethrough so as to provide a path for fluid flow between the inside and outside of the tyre cavity; the device having an first elongate portion adapted to protrude through the valve hole of the wheel when the apparatus is use, and which houses a valve for controlling fluid -14 -flow through the channel, and the light source; and a second portion which in use, sits within the tyre cavity and carries the sensor.
6. Apparatus according to claim 5 wherein the device comprises a moulding into which the valve and light source are embedded.
7. Apparatus according to claim 6 wherein the means effective to receive the output of the sensor and effective to activate the alerting device when the pressure within the tyre is determined to be below a perceived safe level comprises circuitry which is embedded in the moulding within the portion housed within the tyre cavity.
8. Apparatus according to claim 6 or 7 wherein the electrical connection is embedded into the moulding.
9. Apparatus according to any claim 5 to 8 wherein a portion of the device in which the light source is housed is see-through or translucent.
10. Apparatus according to claim 9 wherein the see-through or translucent portion is shaped to act as a lens.
11. Apparatus according to any claim 4 -10 wherein the light source comprises multiple lights positioned around the valve member.
12. Apparatus according to claim 1 wherein the alerting device comprises a light source located within the tyre cavity, and the apparatus comprise means to guide the light to a light projecting means outside of the tyre cavity.
13. Apparatus according to claim 12 wherein the projecting means is a light-guide collar.

-15 -
14. Apparatus according to claim 1 having means to automatically calibrate the perceived safe level upon inflating the tyre.
15. Apparatus according to claim 1 or 14 comprising: Means using the sensor to periodically sense pressure within the tyre cavity and to compare the sensed pressure with a stored value; and means to record a calibration pressure when the comparison of the sensed pressure with the stored value indicates that the tyre has been inflated
16. Apparatus according to claim 15 comprising means to sense the pressure a further time and to use this further sensed pressure to record a calibration pressure.
17. Apparatus according to claim 16 comprising means to take multiple further sensed pressures and to use at least one of these to record the calibration pressure, once two consecutive further sensed pressures are equal or within an acceptable range.
18. A method of calibrating a tyre pressure warning device comprising: sensing the pressure within a tyre cavity and comparing the resultant sensed pressure value with a stored value; if the comparison of the sensed pressure value with the stored valued indicates that the pressure within the tyre cavity is equal or above a threshold pressure, sensing the pressure one or more further times and using one or more of the resultant further sensed pressure values to record a calibrated pressure value.-16 -
19. A method according to claim 17 comprising sensing the pressure multiple further times and using at least one of these resultant sensed pressure values to record a calibrated pressure value when consecutive sensed pressure values indicate that the pressure within the tyre cavity has not changed, or has changed within an acceptable range.