Patent Application
20090066496
The embodiments of the present invention described herein generally relate to a tire pressure monitoring (TPM) wheel sensor unit in a TPM system.
Tire pressure monitor (TPM) sensors generally detect tire pressure information for tires on a vehicle. The TPM sensor transmits the tire pressure information as a radio frequency (RF) signal to a TPM receiver. The TPM receiver processes the tire pressure information and sends out tire pressure messages over a multiplexed bus protocol to an instrument cluster or any other electronic module in the vehicle. The instrument cluster or other electronic module provides the tire pressure status on a display for a user.
Each TPM sensor in the vehicle includes a low frequency (LF) receiver for receiving a plurality of modulated LF messages. Original Equipment Manufacturers (OEM) generally require that the TPM sensors are configured to respond to the plurality of modulated LF messages for diagnostic testing and/or operational purposes. Additional circuitry and software has to be added to the TPM sensor to ensure that the TPM sensor has the capability to respond to all of the modulated LF messages. For example, each TPM sensor may need additional circuitry and software for demodulating and decoding modulated data in the LF messages. In some cases, the TPM sensor throughout its life span, may seldom be required to respond to all of the modulated LF messages as set forth by the OEMs. Some of the modulated LF messages may be rarely used or not used at all.
Each TPM sensor also includes a microcontroller and an over-voltage protection circuit. The microcontroller and the over-voltage protection circuit are implemented as an application specific integrated circuit (ASIC). The ASIC is a customized circuit that may simplify circuit board design and reduce manufacturing costs. The LF receiver may be integrated into the ASIC design or implemented as a standalone circuit. While ASIC designs may reduce manufacturing costs, the costs savings may be offset due to fabrication costs associated in producing an ASIC for a specific application.
Accordingly, it would be desirable to provide a TPM sensor that is inexpensive to develop and supports predetermined diagnostic, testing and operational requirements as set forth by OEMs.
In one embodiment, a tire pressure monitoring (TPM) system for a vehicle is provided. The system comprises a TPM receiver, a trigger device and a TPM sensor. The TPM receiver is adapted to receive tire pressure information. The trigger device is adapted to generate a low frequency (LF) unmodulated signal that is indicative of trigger command. The TPM sensor comprises an LF tank circuit adapted to receive the LF unmodulated signal and a microprocessor operably coupled to the LF tank circuit and configured to detect the presence of LF unmodulated signal and to transmit a LF output signal having tire pressure information to the TPM receiver in response to the trigger command without demodulating the LF unmodulated signal.
In another embodiment, a tire pressure monitoring (TPM) sensor in a vehicle is provided. The TPM sensor is capable of communicating with a trigger device that generates a low frequency (LF) signal unmodulated signal that is indicative of a trigger command. The sensor comprises an LF tank circuit and a microprocessor. The LF tank circuit is adapted to receive the LF unmodulated signal. The microprocessor is operably coupled to the LF tank circuit and adapted to detect the presence of the LF unmodulated signal and to transmit an RF output signal having tire pressure information in response to the trigger command without demodulating the LF unmodulated signal.
A tire pressure monitoring (TPM) sensor in a vehicle is provided. The TPM sensor is capable of communicating with a trigger device that provides at least one low frequency (LF) modulated input signal. The sensor comprises an LF tank circuit, a microprocessor and a compare circuit. The LF tank circuit is adapted to receive the LF modulated input signal at a predetermined frequency. The microprocessor is operably coupled to the LF tank circuit and is adapted to demodulate the LF modulated input signal, to decode data present in the LF modulated input signal and to generate an LF output signal in response to the decoded data. The comparator is operably coupled to the LF tank circuit and is adapted to receive the LF modulated input signal and to provide the LF modulated input signal to the microprocessor in response to the comparator determining that the LF modulated input signal is a valid signal.
The present invention is pointed out with particularity in the appended claims. However, other features of the present invention will become more apparent and the present invention will be best understood by referring to the following detailed description in conjunction with the accompany drawings in which:
The trigger device 12 may include any number of devices for generating a plurality of trigger commands. Such trigger commands (or trigger signals) are generally defined as messages or commands which require the TPM sensor 14 to perform a particular function. Such functions may be for operational, diagnostic and/or testing purposes. The trigger device 12 transmits the trigger commands as radio frequency (RF) modulated input signals. In one example, the RF modulated input signals may be low radio frequency (or low frequency) (LF) amplitude shift key (ASK) modulated onto an envelope of a carrier wave at a predetermined frequency. In one example, the predetermined LF frequency may be 125 kHz. The particular frequency, for the carrier wave may be varied based on the desired criteria of a particular implementation.
The trigger circuit 12 may include an initiator that is configured to trigger operation of the TPM sensor 12. The initiator is generally positioned within the vehicle. For example, during vehicle startup, the initiator may send the LF modulated input signal to a particular TPM sensor 14 in the vehicle to trigger the TPM sensor 14 into transmitting data to the TPM receiver 16 for a particular tire. Such a process may be exhibited when configuring a particular TPM sensor to a particular wheel so that the TPM receiver 16 has knowledge of which TPM sensor 14 is positioned within a particular wheel. The TPM receiver 16 may send multiplexed messages over a multiplex bus to the instrument cluster (or other module in the vehicle) to provide pressure and other information for a specific tire. Vehicles may or may not include an initiator. The implementation of the initiator on a vehicle may vary based on the type of vehicle used.
The trigger device 12 also comprise a number of diagnostic based hand held tools. For example, the trigger device 12 may be a diagnostic tool used by personnel in dealerships, vehicle assembly plants, or wheel supplier plants to communicate with the TPM sensor 14. The trigger device 12 may also be an end of line (EOL) tester that is used to test the integrity of the TPM sensor 14 during the assembly of the TPM sensor 14 or during the assembly of the vehicle.
The trigger device 12 (e.g., EOL tester or the hand held test tool) may transmit trigger signals as diagnostic commands in the form of the LF modulated input signals to the TPM sensor 14 and wait for a response from the TPM sensor 14 to confirm operational integrity. The trigger device 12 may also request that the TPM sensor 14 provide responses LF modulated input signals for diagnostic purposes. The responses may include that the TPM sensor 14 provide diagnostic information such as factory mode information, tool mode information, software revision-level, message data, preamble data and check sum information or other suitable diagnostic responses. The trigger device 12 may also request that the TPM sensor 14 transmit tire pressure information or other information on-demand as opposed to waiting for the next periodic event for the TPM sensor 14 to transmit the information.
A motion sensor 28 is also integrated into the TPM sensor 14. The motion sensor 28 wakes up the microcontroller 22 as the tire starts to rotate. The TPM sensor 14 transmits data as RF output signal to the TPM receiver 16 in response to the tire rotating. The RF output signal may be a low RF output signal. The TPM sensor 14 provides tire pressure information and other information even after the key is out of the ignition (e.g., when the vehicle is in a sleep mode). The TPM sensor 14 provides the tire pressure information periodically while the vehicle is in the sleep mode. In one example, each periodic event may be minutes apart from each other to preserve battery life. An ASIC may be fabricated to include all of the components 20, 22, 24, 26, 28 and 30 or any one or more of the components 20, 22, 24, 26, 28 and 30.
An over-voltage protection circuit 40 is coupled to the LF tank circuit 26. An input 42 of the microcontroller 22 is coupled to an output of the over-voltage protection circuit 40. The over-voltage protection circuit 42 includes a diode D1 and a resistor R1 to protect the microcontroller 22 in the event the LF tank circuit 26 receives a large voltage amplitude from an LF field present in the LF modulated input signal. Diode D1 limits the input voltage to the microcontroller 22. The diode D1 may be implemented as a Schottky diode. Resistor R1 limits the flow of current to the microcontroller 22.
The microcontroller 22 generally comprises an ASIC. The microprocessor 22 includes a compare circuit and a logic circuit 52. The compare circuit includes a comparator 44 or any other circuit configured to compare the voltage input (e.g., input to the microcontroller 22) to a predetermined voltage and to generate a voltage output based on the voltage input and the predetermined voltage. The input 42 is coupled directly to a negative input pin of the comparator 44. A positive input pin is coupled to voltage reference (Vref). Vref may be calibrated to a particular voltage via software. The particular voltage value of Vref may be varied based on the desired criteria of a particular implementation. The comparator 44 provides a voltage on an output pin 46.
An envelope detection circuit 48 is coupled to the output pin 46. The envelope detection circuit 46 includes a diode D2, a resistor R2, a capacitor C2 and the logic circuit 52 of the microcontroller 22. The diode D2 is adapted to clamp voltage on the output pin 46. In one example, diode D2 may be a Schottky diode. Resistor R2 and capacitor C2 form a low-pass filter to define a frequency window for allowing specified frequencies of the signal to pass to the logic circuit 52 via an output 50. Port pin on the microcontroller 22 receives the filtered signal from the low-pass filter. The low-pass filter and the logic circuit 52 coact with each other to demodulate and decode the LF modulated input signal.
In operation, the tank circuit 26 receives LF modulated signals from the trigger device 12. The data on the LF modulated input signal may be ASK modulated onto a carrier wave having a radio frequency of 125 KHz. The over-voltage protection circuit 40 protects the input 42 to the microcontroller 22 in the event the LF field in the input signal generates a large input voltage. The input voltage is presented to the negative input pin of the comparator 44. The comparator 44 compares the voltage of the negative input pin to Vref to ensure that the incoming voltage from the LF field is not noise. If the voltage at the negative input pin is larger than Vref, then the comparator 44 outputs a high voltage on the output pin 46. If the voltage at the positive pin is less then Vref, then the comparator 44 outputs a low voltage on the output pin 46. Vref is generally a calibratable value configured by software in the microcontroller 22. Conventional TPM sensors generally include operational amplifiers and filters to increase the amplitude of the LF field to ensure that the incoming LF field is not noise. The implementation of the comparator 44 provides for a low-cost alternative to such an approach, as the comparator 44 is able to detect the presence of a valid field by comparing the incoming voltage to a predetermined voltage without the need to increase the amplitude of the LF field.
The voltage output of the comparator 44 is passed through the low-pass filter where high value frequencies are filtered and low frequencies are passed to the microcontroller 22 via the Port pin. The microcontroller 22 demodulates and decodes data present in the LF modulated input signal.
While the microcontroller 22 is generally adapted to detect the presence of the LF field in the LF modulated input signal, the microcontroller 22 is not capable of reacting to the LF field alone. The microcontroller 22 and the envelope detection circuit 48 demodulates the modulated input signal and decodes data present within the LF modulated input signal in order for the TPM sensor 14 to transmit the RF output signal.
In general, the TPM sensor 14 is configured to decode a plurality of trigger commands transmitted as LF modulated input signals by the trigger device 12. The TPM sensor 14 may demodulate and decode the data in the LF modulated input signal and transmit a particular RF output signal in response to the data in the RF modulated input signal. The diagnostic commands modulated on the input signal may include but not limited to factory mode information requests, tool mode information requests and software mode information requests. The TPM sensor 14 may provide such information and other data related to operation of the TPM sensor 14.
In operation, the tank circuit 26 receives the LF field at the corresponding frequency. The overvoltage protection circuit 40 protects the microcontroller 22 in the event voltage from the LF field is large. Resistor R1 limits the amount of current delivered to the microcontroller 22. Voltage from the LF field is presented to the negative pin of the comparator 44. The comparator 44 compares the voltage at the negative input pin to Vref to differentiate between a true voltage level or noise that may be present in the input signal. If the voltage at the negative input pin is larger than Vref, then the comparator 44 outputs a high voltage on the output pint 46. If the voltage at the positive pin is less then Vref, then the comparator 44 outputs a low voltage on the output pin 46. As noted in connection with
A high output voltage on the output pin 46 may be indicative of a valid LF field. In response to detaching a valid LF field the sensor 14′ may transmit data on the RF output signal. Such data that may be transmitted on the LF output signal may include tire pressure information, sensor IDs, software revision levels, check sum data, temperature data, battery power level, preamble data and/or all diagnostic responses generally required by OEMs. The sensor 14′ may transmit all of the mentioned information and more on a single RF output signal.
The sensor 14′ provides a low-cost alternative in comparison to the sensor 14 as described in connection with
While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.
