Tire-pressure monitoring system

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A Tire Pressure Monitoring System (TPMS) is generally an electronic system designed to monitor the air pressure inside all the pneumatic tires on automobiles, aeroplane undercarriages, straddle-lift carriers, forklifts and other vehicles. The system is also sometimes referred to as a Tire Pressure Indication System (TPIS). These systems report real time tire pressure information to the driver of the vehicle - either via a gauge, a pictogramme display, or a simple low pressure warning light.

Contents 1 Types 1.1 Direct 1.2 Indirect 2 History 3 Direct TPMS Technology 4 Tire Pressure Markets 4.1 Light Duty vehicles <26001 pounds 4.2 Heavy Duty vehicles class 7-8 GVW > 26000 pounds 5 Setting up the system 6 Performance 7 References 8 See also

[edit] Types

[edit] Direct

Direct sensor TPMS: These systems employ physical pressure sensors inside each tire, and a means of processing and sending that information from inside the tire to the vehicle's instrument cluster. There are two main types of direct tire pressure monitoring system currently in use. These are known as 'high line' and 'low line'.^[1]

Direct sensor TPMS can identify simultaneous underinflation in all four tires in any combination.

Direct sensor TPMS are specifically designed to cope with the effects of changes in tire pressure due to ambient temperature changes and road to tire friction based temperature changes. Friction between the tire and road surface heats up the tire and increases the pressure in the tire. The alarm activation threshold pressures are usually set according to the manufacturers recommended "cold placard inflation pressures".

In order to transfer data from a rotating wheel, Direct Sensor TPMS may use a Radio Frequency (RF) communication channel or an electromagnetic coupling means to overcome the tire/chassis rotational boundary.

The pressure sensor devices of Direct sensor TPMS may be either battery powered or batteryless: Battery powered Radio Frequncy based TPMS have several disadvantages. Batteries eventually become exhausted and represent a maintenance cost to the consumer. Batteries are chemical systems with lifetimes that unfortunately perform very poorly in extreme temperature environments typical of North America and European climates and in aerospace applications. In order to conserve battery life and to conform to various countries communication authority standards for short range radio communications, the power levels of battery powered TPMS are kept very low . As a consequence of these very low power levels, the construction of certain steel belted radial replacement tires and vehicle metallic geometries can block the low power signal transmission paths.

Other disavantage of battery powered direct sensor TPMS are that their physical sensors are quite large and are either mounted on the end of valve stems or by a steel band around a rim's dropwell center. In both cases, these sensors affect a wheel's balance are subject to damage during tire removal and fitting procedures. Banded sensors may also damage the tire bead's air seal. So-called total cost of ownership for direct systems is much higher than for indirect systems due to battery and wheel changes and broken/damaged parts.

On the other hand Batteryless Direct Sensor TPMS overcome these limitations and have the advantage of being maintenance free. Unfortunately, these systems are not available yet on the passenger vehicle market.

[edit] Indirect

Indirect TPMS do not use physical pressure sensors. Indirect TPMS measure the "apparent" air pressure, by monitoring individual wheel rotational speeds, and other signals available outside the tire itself. Most indirect TPMS use the fact that an under-inflated tire has a slightly smaller diameter than a correctly inflated tire and therefore has to rotate at a higher angular velocity to cover the same distance as a correctly inflated tire. Newer developments of indirect TPMS can also detect simultaneous under-inflation in up to all four tires using vibration analysis of individual wheels or analysis of load shift effects during acceleration and/or cornering, which can be realized in software using advanced signal processing techniques. However, the vibration analysis technique requires the use of additional suspension sensors which result in increased complexity and cost of the overall system as long as vertical chassis movements are concerned. That is why most current advanced indirect systems use the spectral content of the wheel speed sensor signals so no additional sensors are needed and the computations can also be carried out by usual processors for example in usual ABS or ESC control units.

Indirect TPMS are realized in software in combination with wheel speed sensors for anti-lock braking systems, and electronic stability control systems. A disadvantage of indirect TPMS is that the driver must calibrate the system by pushing a reset button on the dashboard or through the on-board computer and if this is performed when any tire is in an under inflated condition then the system will not report correctly.

[edit] History

The first passenger vehicle to adopt Tire Pressure Monitoring (TPM) was the Porsche 959 in 1986, using a system developed by PSK^{[citation needed]}. Major TPMS manufacturers are 'Continental AG' , Schrader Electronics, 'Advantage PressurePro LLC' ^[2]',' 'Lionax Inc.' ^[3]',' Stemco's BatRF' ^[4]', 'SmarTire Systems', 'Shanghai Baolong Industries', 'Wi-Gauge wireless TPMS', [Hangsheng Electronics Corp]HSAE,Siemens VDO, Beru AG, TRW Automotive, 'ETV Corporation PL' (VisiTyre)^[5], , 'Pacific Industries', 'Schrader-Bridgeport'^[6], 'EnTire Solutions LLC', 'NIRA Dynamics AB' (Tire Pressure Indicator), 'Transense Technologies plc', IQ-mobil GmbH (RDKS)^[7], and APRI s.r.o.,'ste engineering'^[8].

Due to vehicle safety and maintenance economy, TPMS appeared more widely in Europe as an optional feature for top range luxury passenger vehicles, like the Audi A8, Mercedes-Benz S-Class and the BMW 7 Series. In 1999 the PSA Peugeot Citroën decided to adopt TPM as a standard feature on the Peugeot 607. The following year (2000), Renault launched the Laguna II, the first high volume mid-size passenger vehicle in the world to be equipped with TPM as a standard feature.

The Firestone recall in the United States in the late 1990s which was attributed to more than 100 deaths from rollovers following a tire tread-separation, pushed the Clinton administration to publish the TREAD Act. This act mandates the use of a suitable TPM technology in order to alert drivers of a severe under-inflation condition of their tires. This act affects all light motor vehicles (<10,000 lb) sold after 1 September 2007.

Phase-in started in October 2005 at 20%, and reached 100% for models produced after September 2007. While in the US, TPMS legislation grew from safety-related motives, European Union (EU) and Far East legislators are looking at TPMS as a way of reducing CO₂emissions, and are presently considering compulsory Tire Pressure Monitoring Systems from this environmental stance.

Regardless of US and EU legislation, the introduction by several tire manufacturers of run flat tires makes it mandatory for car manufacturers to fit a system where the drivers are made aware the run-flat has been damaged. The run-flats are designed to be used at no more than 80 km/h (50 mph) for no more than a distance of 80 km, and this is why it is mandatory that runflats are monitored by TPMS. They have received a mixed reception from the public due to their impact on comfort with a harder ride.

Lastly, the most recent advance with TPMS technology is the introduction of Battery-less Direct sensor systems which require zero maintenance and are very reliable. VisiTyre ^[5] is the first of this new class of battery-less TPMS which allows pressure on demand readings immediately from ignition and unlike radio frequency TPMS systems is also transparent to all tire construction types.

Another milestone has been the launch of the Audi A6 model year 2009 in the US with the first indirect TPMS to comply with the US TPMS legislation.

[edit] Direct TPMS Technology

In the early days of development TPMSs were implemented using radio frequency technology, to avoid expensive and rather complicated rotating contact wiring, together with an electronic control unit fitted inside the vehicle, which provides the necessary processing functionality to interpret pressure data coming from battery powered sensor transmitters within tire cavities. The system delivers alerts and warnings to the driver.

Companies like Schrader Electronics designed first generation TPMSs using battery powered radio transmitters, with sensors mounted on a standard tire valve, and a chassis mounted radio frequency receiver, whose functions can also be integrated in other radio-frequency units mounted on the vehicle, such as Remote Keyless Entry receivers, and Body Control Units.

Typical RF TPM systems employ four or five battery powered transmitter-sensors,^[9] one RF receiver (either stand-alone or integrated in other vehicle electronics), and some other satellite hardware which can perform the function of identifying the tire position involved in the inflation anomaly. Each tire pressure sensor can periodically trigger a transmission of pressure status, or be polled continuously on demand. The most technologically challenging part of the system is the conservation of battery power used by the RF transmitter-sensor. Most RF based TPM sensors on the market today use a battery, a silicon-based pressure sensor, and an RF oscillator (either SAW- or PLL–based).

Automakers require a battery lifespan of between seven and ten years, so TPMS system designers use power saving techniques to extend the battery life. The heart of the sensor is a silicon application-specific integrated circuit (ASIC) chip, which can manage critical power saving algorithms and other functions of the sensor. However, there remains the fundamental problem that all batteries eventually become exhausted with the result that the consumer is faced with flat battery problems as well as flat tire problem. The battery represents safety and replacement cost issues for the consumer. Vehicle manufacturers are also concerned about costly warranty claims and litigation that may result if injury and loss of property occur as a consequence of RF based TPMS battery failures.^[9]

In the US, there are approximately 16 million new passenger vehicles manufactured annually, which must ultimately comply with the legislative requirements of the TREAD Act, and be fitted with TPMS. If each vehicle has four or five wheels fitted with battery-powered RF TPMS wheel modules there could be more than 65 million batteries introduced annually into the environment. Disposal of the batteries in such a widespread consumer application is a minor environmental concern compared to the other wastes from automobile operation.

To overcome the battery issues a new generation of batteryless TPMS is being developed by two companies using quite different technologies. Transense is promoting a SAW-based technology. VisiTyre is using an electromagnetic close-coupling technology to effectively eliminate the battery. VisiTyre batteryless TPMS is in pre-production preparation for supply and integration into model year 2009 vehicle platforms. Transense has licenced its technology to several automotive companies but it is not yet commercially available for OEM passenger vehicles.

Other developments with TPMS include research into the use of energy harvesting devices which may lead to future types of batteryless TPMS.

Recently STE Engineering, a company based in the North of Italy, introduced a new class of OEM oriented TPMS tire stem whose concept is basically the integration of a simple hybrid ceramic circuit inside the body of a standard tire stem, as opposed to traditional TPMS which have an electronic PCB located in a dedicated plastic box, just beneath the tire stem itself ^[10]. Advantages of this solution are obviously connected to the use of an ISO-TS qualified tire stem, as normally used in the automotive market, allowing huge cost savings and enabling standardization of remote direct TPMS. Due to extremely reduced power consumption, measured to be about three orders of magnitude low power less than standard technologies, this new application allows use of reduced size battery cells— in fact, now a 12.5 mm diameter standard cell can replace the 20 mm cell normally used. STE says that, being able to "survive" fed by the very small energy harvesters devices are able to generate, this new technology approaches the highly desirable "Battery-less" operating condition; Other benefits are: reduced overall weight, mechanical robustness, cost reduction, and extended temperature range (-40° +125°C).STE concept introduces a new methodology which sees in-stem electronics rather than "attached-to-the-stem" technology: the high grade of integration has been achieved through a substantial reduction of components with benefits in terms of costs savings and enhanced mechanical robustness. The PM17, that's the name of the new concept of tire stem, has demonstrated to be able to improve supply chain performances with regards of production planning and logistics: the similarity of PM17 tire stem to traditional mechanical valves normally available on the market, well support OEM's planning of risks reduction due to non-conformal mounting processes, after-market and after-sales strategies: the procedure of installing a PM17 TPMS wheel unit clearly avoids weird procedures used to couple tire's bid with rims when mounting standard "butterflied" TPMS. The PM17 tire stem has been recently demonstrated during the IVth international Intelligent Tire Technology conference in Wiesbaden (October 2008)

[edit] Tire Pressure Markets

[edit] Light Duty vehicles <26001 pounds

Tire pressure sensors in this market are usually based purely on cost and installed by the OEM. The Tread Act applies to these vehicles.

[edit] Heavy Duty vehicles class 7-8 GVW > 26000 pounds

There is another class of vehicles though where most of the above mentioned systems do not really work well and other systems have been developed. The main issues on a large vehicle is that quite often it is unknown which wheels will be attached to a given tractor at any given point in time, also the trailer manufacturers and tractor manufactures have not standardized on similar systems. RF systems for these units must also work over much longer ranges, which may force repeater systems to be installed on the tractor or trailer. It is expected that battery lives on these systems should be in the 5-7 year range since the cost of breaking down a tire can be so much more expensive. The Department of Transportation max loading requirements forces trailer manufacturers to spread loads over multiple axles giving rise to typical trailers with 8-12 tires but this can reach as high as 96 tires on specialty haulers. The Tires carcasses can have lifetimes of up to 8 years through multiple retreading processes. This has given rise to a specialized industry that focuses solely on the issues found in the trucking industry.

Central inflation systems originally claimed to have solved these issues however they have not yielded a complete solution since they do not solve all the issues (i.e. no support for the steer axle) and they bring new issues with maintenance of the rotary couplings in the hub caps. Furthermore the inflation systems may cover a slow leaking tire issue long enough for a tire to become completely destroyed because the penetrating object is not removed thus shortening the life of the tire it is trying to save. Some major Inflation systems are Meritor PSI, Hendrickson international and Vagia used mostly in South America.

In order for a tire pressure sensor to be completely effective it must have several capabilities to allow for the various maintenance personnel groups to use them. First, each driver is required to do a pre-trip inspection so it is nice if the tire pressure monitor has some indicator that can be read without tools just by looking at the wheel.

Second, it usually should have the capability to cover dual sets of tires in some fashion. It is also nice if the fill points can be centralized so that airing can be done easily without reaching through the small hand holes in the rims.

Thirdly, they need to have some wireless communication system that has a reasonably long range and a long battery life. It is important that sensor regularly communicates as an I’m alive condition, since having a dead sensor can be worse than having a no sensor at all if everyone thinks the monitoring is being taken care of automatically.

In cab tire pressure monitoring can still be valuable for the tractor/trailer combinations but these systems must have the capability to adapt to changing of tires and trailers without operator intervention. It is important to find ones with long ranges since repeater systems can add tremendously to the cost. These systems alert the driver to the hazardous blowout condition, however, even these new systems still may not help larger fleets deal with slow leaking tires, because the driver may ignore a slow leaking tire and not tell fleet maintenance personnel about the issue until it is too late. This has given rise in recent years to monitoring solutions that track the tire condition and send back alerts to fleet maintenance personnel that allow for them to schedule maintenance on the slow leaking tire on an exception basis instead of having to check each tire manually. Many fleets today admit that tire pressure checking is a major problem in enforcement. Most have policies in place requiring the regular check of every tire, however, the practice is not terribly effective because of the shear scope of the issue and the fact that it is hard to get a complete record of all tire checking. Today the best systems consist of automated data collection systems. Some of these use gate readers that automate the collection of tire data back to a databases or to web portals that allow maintenance operators to see the entire fleet at a glance. For long haul fleets that may not see their vehicles for long periods of time, a centralized reading system may not work but there are emerging systems that aggregate the tire pressure sensor data back to the asset tracking systems so that alerts can be sent back to the main office when an issue arises. For small fleets, handheld devices exist that allow for the person checking tires to simply walk around vehicles and collect the data for downloading to a central database allowing for enforcement and trending to be done without errors. Some of the automotive manufacturers have attempted to broaden their scope into the heavy duty markets but a few manufacturers have focused solely on this market. 'Stemco's BatRF' ^[11]' and Wabco.

[edit] Setting up the system

The TPMS has to be installed and tested in the vehicle manufacturing environment. The process is generally as follows. The TPMS sensors are attached to the wheel during the wheel and tire assembly process. The wheels are then attached to the vehicle. This is the first point at which the TPMS can be clearly associated with the vehicle^{[citation needed]}. In the case of battery powered RF systems, it is on this final car assembly line that RF antennas are used to extract the unique IDs of the TPMS. These IDs, and their associated wheel position on the car are downloaded to the vehicle Engine Management Unit^{[citation needed]}. This enables warnings to be associated with wheel position.

Similarly, the franchised car dealer workshop needs to have portable tools available to extract the wheel sensor ID, and in the case of battery powered TPMS, reprogram the car's ECU as would be required for wheel sensor module replacement when a battery fails. Service to the vehicle tires may also require replacement of a TPMS sensor due to valve core corrosion, a broken band, or other issues.

When a TPMS sensor is replaced, it is important to understand your vehicle. Every manufacturer has a different method to reprogram the vehicle. Some vehicles simply reprogram themselves while you drive. Others require the user to perform an action, such as turning the key and pressing a pedal, or using the key-fob to trigger a re-learn mode. Not all vehicles may be placed into a re-learn mode— some require an extra interface to the vehicles OBDII/CAN-BUS to speak with the vehicle ECU, BCM or other device^{[citation needed]}. Vehicles with this interface require the user to return to the dealership for a tire rotation^{[citation needed]}.

Direct sensor batteryless TPMSs, such as the VisiTyre system, are zero-maintenance direct sensor TPMS that do not require any recalibration after tire replacement or tire rotation.

[edit] Performance

A TPMS helps to improve vehicle safety, and aids drivers in maintaining their vehicle tire pressures. Properly maintained tires help with vehicle safety, performance and economy. In the US, the National Highway Traffic Safety Administration (NHTSA) has estimated that every year, 533 fatalities are caused by tire defects in road accidents^{[citation needed]}. Adding TPMS to all vehicles could avoid 120 of the 533 yearly victims and spare as many as 8,400 injuries every year^{[citation needed]}.

The French Sécurité Routière (Road Safety organization) estimates that 9% of all road accidents involving fatalities are attributable to tire under-inflation^{[citation needed]}, and the German DEKRA estimated that 41% of accidents with physical injuries are linked to tire problems^{[citation needed]}.

On the maintenance side, it is important to realize that fuel efficiency, and tire wear are severely affected by under-inflation. In the US NHTSA data relates that tires leak air naturally and over a year a typical new tire can lose between 20 and 60 kilopascals.

If we also consider that over 40% of vehicle owners in Europe and North America check their tires less than once a year^{[citation needed]}, it is conceivable that 40% or more of vehicles currently in use in those areas are running with underinflated tires.

The European Union reports that an average under-inflation of 40 kPa produces an increase of fuel consumption of 2% and a decrease of tire life of 25%. The EU concludes conclude that tire under-inflation today is responsible for over 20 million liters of unnecessary burned fuel, dumping over 2 million tonnes of CO₂in the atmosphere, and 200 million tires prematurely wasted in the world.

For these safety and environmental reasons, the US Federal government has mandated the use of TPMS, and other countries should follow closely. The TPMS mandated by the US law must warn the driver when a tire is under-inflated by as much as 25% {Ref: US DOT NHTSA Docket No 2005-20586}. However, since the recommended tire pressures for most vehicles are more than 160 kPa (23 psi), a deflation of 40 kPa would be within the 25% allowance and would not trigger the TPMS warning mandated by the U.S. law. Therefore, the mandated TPMS is mainly designed for safety and is unlikely to deliver the above benefits. Drivers are still advised to manually check their tire pressure often to maintain optimal performance.

In the case of battery powered TPMS, at some point in the vehicle's lifetime, every battery will ultimately become exhausted and there will be an ‘unsafe’ window where the system is unavailable. Battery lifetime is adversely affected by sub zero temperature extremes which occur in certain areas of Europe and North America. Hence, vehicle manufacturers are showing a great interest in the next generation of battery-less TPM systems being developed by Transense and VisiTyre.

Generally speaking, direct tire pressure monitoring systems may offer the following features:

• Measure (and may display) tire air pressure, with an accuracy able to detect under-inflation conditions of less than 25% of the recommended cold inflation pressure
• Measure and display tire air temperature (optional)
• Locate Tire involved in pressure defect (optional)
• React to fast and slow leaks (< 5 s) for early warning
• Do not require initialization or zero button, i.e., self learning (optional)
• Can monitor spare tire pressure{Ref: VisiTyre Batteryless TPMS}
• Can monitor tire pressure when stationary (Direct TPMS only).

[edit] References

• Tire Rack article: Tire Pressure Monitoring System.

[edit] See also

• Cold inflation pressure
• Run flat tire
• Tire-pressure gauge
• Car safety