Direct TPMS , or a direct tire pressure monitoring system (TPMS direct sensor) refers to the use of pressure sensors directly mounted on wheels or vehicle tires. Pressure inside the tire is measured using a pressure transducer with pressure information which is then sent to the vehicle to alert the driver under or over tire inflation. Pressure information is usually transmitted to vehicles using radio frequency (RF) technology, although systems using mechanical, electrical or magnetic methods have been used for the past few years.
Video Direct TPMS
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In the current design of direct TPMS, small electronic assemblies that are rugged enough to be mounted inside the tire, measure pressure using a microelectromechanical pressure sensor (MEMS) and then transmit this and other information to one or more vehicle receivers. Other information may include the serial number, temperature, acceleration, and status of a complete tire pressure monitoring system. The purpose of the serial number is to allow the vehicle to ignore the transmission from another vehicle and to operate with a unique data field. The distinctive direct TPMS (eg Ford, BMW, or Toyota) consists of the following components on the vehicle:
- TPM sensor directly mounted behind the valve rod on each wheel
- TPM Warning Light
- Unique identifiers (ID) whose tires provide data including speed and direction of rotation
- Monitor the wind pressure of the electronic control unit (ECU)
- Antenna (s)
- Controls for periodic measurements
- Resources
- Diagnostics and build system
Most TPMS systems directly use ultra high frequency radio (UHF) in one of the 'unlicensed' (industrial, scientific and medical ISM bands) to transmit data, often around 434 MHz in Europe and 315 MHz in many other countries in the world.. In some systems there is a separate receiver or antenna near each wheel while more commonly there is a single receiver that receives data from all wheels on the vehicle. Generally these receivers are also used for remote keyless entry systems (RKE) as these also typically use UHF radio transmissions.
The TPM sensor can be mounted to the wheels in several ways. They can be mounted behind a tire valve rod or mounted by adhesive or to a ribbon which is then secured safely around the tire inside the tire, usually in the descending zone.
Direct tire pressure monitor system light
When the TPMS direct warning light is on, one of the tires is under inflation, over-inflated, or there is a system error. If the light is constant then inflating the correct placard pressure should turn it off. If this does not happen then this shows a puncture. If the light is intermittent or if it remains lit after the correct inflation or replacement of a leaky tire then this indicates an error with the TPMS system directly.
Register TPMS ID directly
When the TPMS system is installed directly at the factory, the unique ID number of the TPM sensor (tire pressure monitoring) must be registered together with its position in the vehicle with the tire pressure ECU monitor. This is also the case if one of the system components is then changed, ie. in terms of rotating tires, changing sensors, replacing ECUs, etc.
This process requires active TPMS sensor activation using low frequency radio (LF) and transmitted UHF data retrieval. These data include direct TPMS ID, pressure and temperature. In automotive manufacturing factories, activation is done using a large antenna system while at dealers and tire stores, hand tools are used. These tools can also be used to check the TPMS directly for errors before unloading. If the TPM sensor or its position in the car is changed without re-registering the ID, the TPMS warning light will light up and stay on until the ID is re-registered.
Maps Direct TPMS
Localization
If there are multiple antennas or receivers, this allows TPM localization so that the vehicle can tell where the pressure data wheels are coming from. As an alternative to this method, the vehicle can be programmed at the time of manufacture with the tire position along with its TPM serial number. This allows the vehicle to display which tires have low pressure.
Also, some vehicles have low frequency radio transmitters installed near each wheel that can be used to force individual TPMs to transmit at will. It typically uses a similar technology for the 125 kHz RFID tag in which the transmitted field is dominated magnetically and can be easily detected by small LF antennas located on the TPM. This localization method is often referred to as a high-level system.
LF antennas are also often used by TPM for configuration and for forcing transmission so that localization can be re-studied by the vehicle if the sensor is changed or the wheel is rotated even up the tread wear.
The third method uses a UHF signal strength proportional to the TPM distance from the receiver. If the receiver is located in front of the vehicle, the signal from the TPM front wheel will be stronger than that of the wheel behind.
TPM also has a method of detecting the direction of rotation of each wheel to identify which side of the vehicle the TPM is located and this information forms part of the message delivered to the vehicle. This combination allows the correct wheel to be identified.
TPM sensor features
The TPM sensors currently installed in high-volume production cars around the world are battery-powered, self-contained units that periodically measure tire pressures, and often temperature and acceleration. This sensor is equipped with an RF transmitter circuit used to broadcast the measured pressure, etc. Inside the tire.
TPM is designed to use the power as small as possible to provide the maximum battery life. This is done by using very low power circuits and transmitting as little data as possible and with the lowest possible power. UHF transmitters in TPM usually transmit about 250? W (1? W equals one million (10 -6 ) of watts).
TPM does not have a UHF receiver built because of the relatively high power requirements of this technology. This means that they can not say that they are transmitting at the same time as other TPMs. Most TPMs do have LF receivers because they use little or no power.
Pressure sensors, temperatures and accelerations produce analog signals that are converted to their digital equivalent using an analog to digital converter. The acceleration sensor measures the centrifugal force generated when the wheel spins. This force is proportional to the rotational speed. The acceleration sensor may be a simple switch rather than an analog transducer (accelerometer). This is usually referred to as the roll button. The acceleration sensor allows the TPM to be placed in a low-power communication device mode, when a stationary vehicle can extend battery life. The advantage of a roll over accelerometer switch is that the switch is purely mechanical and does not use any power to make measurements.
When the vehicle does not move, the TPM may periodically deliver to the vehicle. This allows (as long as the vehicle receiver is always on) the driver or vehicle operator to warn of low pressure as soon as the Ignition system is turned on rather than having to wait until the vehicle moves.
All TPM units on vehicles operate on the same frequency of RF channels and each message includes pressure data, temperature data, unique ID code, operating status data, status information, and check digits. Check digit is checksum or cyclic redundancy check (CRC).
TPM usually does not have information about the correct tire pressure as this will be very difficult and may be dangerous to support. However it may have an algorithm contained in it that detects both slow and fast changes in pressure. This condition can be transmitted as part of TPM status. It can also cause TPM to send more frequently.
Direct tire pressure monitoring system
There are two main types of direct tire pressure monitoring systems that are in use. These are known as 'high lines' and 'low lines'.
High channel system
If the vehicle is equipped with a low frequency transmitter (LF) near each wheel, the vehicle may use this to force the sensor to transmit. In this case, the TPM can not transmit itself, but the vehicle will periodically instruct the sensor to send their information.
In addition, the TPM will be forced to transmit when the ignition is turned on. This will provide an early indication of low pressure without having to activate the vehicle receiver when the vehicle is not in use. Transmitters are usually activated one by one in sequence so the vehicle can notify the driver of the wheel location with low pressure. This information can then be used to localize by matching the TPM unique ID with its position found by this sequential activation. This method is used on some high-line systems where TPM also transmit periodically.
In some vehicles only three LF transmitters are used to save money. The vehicle assumes that the transmission of the nearest TPM that has not been built by the LF belongs to the TPM located where there is no LF transmitter.
High channel systems are inherently more expensive than low channel systems but they have the advantage of knowing vehicle pressure when starting without draining the vehicle's main battery and providing localization. This system tends to be used in higher end models.
Low channel system
In this system, the TPM unit sends itself at fixed or random intervals. Because individual TPMs in vehicles do not know whether other TPMs are transmitting at the same time, it is possible to have collisions between messages sent. Steps should be taken to ensure that the message is received by the vehicle. On some systems, messages are re-sent multiple times to reduce interference effects (communication). The transmission pattern can be random or pseudo random to reduce the possibility of a collision between the transmission of the sensor on the vehicle.
Another method to avoid collisions is to send more often like once per minute. In addition, if the TPM detects rapid pressure changes or too high temperatures, the TPM will start sending more often so that the vehicle has more opportunities to receive information. Low line systems are used in most vehicles because they cost less.
Legal status
AS
US vehicle TPMS usage is mandated in 2008 by Transport Retrieval, Accountability and Documentation (or TREAD). It states that vehicle drivers should be given an inflation warning under 25%. Warning is shown to the driver in accordance with 49 CFR Part 571 Federal Motor Vehicle Safety Standards (FMVSS). The minimum requirement for warning is in the form of a simple lit symbol on the dashboard, and this is often coupled with a car graphic display showing the wheel position corresponding to the warning light. All new 2008 model light vehicles must have a TPMS (directly or indirectly) installed that is capable of detecting when one or more vehicle tires, up to four tires, is 25% or more under the recommended manufacturer's inflation pressure (pressure plaque) or activation pressure the minimum specified in the standard, whichever is higher.
EU and Far East
The EU and Far Eastern legislators see TPMS as a way to reduce CO2 emissions, and currently (in January 2009) consider a mandatory tire pressure monitoring system of this environmental stance. Starting November 2014 (ECE-R 64 EU Directive), all new models of passenger cars must be equipped, at E.U., with TPMS.
See also
- Cold inflation pressures
- Run a flat tire
- Tire pressure gauge
- Car security
Note
Bibliography
- Hawes, James; Fisher, John; Mercer, Todd (2008), Tire Pressure Monitoring System Monitor, , Mitchel1, ISBNÃ, 1-58718-177-0 .
External links
- Privacy and Privacy Security of Mobile Wireless Networks: Study Study of Tire Pressure Study System
- Media files provide information about live tpms, tpm sensors, and tpms security tools
- NHTSA impact analysis report for tpms
Source of the article : Wikipedia
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