Tire pressure monitoring system transmission protocol
A system for monitoring conditions within a tire includes a sensor assemblies ( 14 ). The sensor assemblies ( 14 ) emit a transmission ( 26 ) containing information indicative of conditions within a tire to a receiver ( 16 ). The transmission ( 26 ) from the sensor assemblies ( 14 ) includes an amplitude shift key wake up portion and various data packet portions. The data packet portions are separated by a variable interval to prevent collisions of transmissions at the receiver.
1. A system for monitoring conditions within a tire comprising;
a sensor disposed within a tire for sensing conditions within said tire;
a transmitter for transmitting a signal indicative of conditions within said tire;
a receiver for receiving said signal;
said signal indicative of conditions within a tire includes a first preamble portion and at least one data packet portion wherein there is a variable interval between the at least one data packet portions, wherein said variable interval varies according to the equation Interval length=Standard length+(beta * standard length)
Where:
interval length is the length of time in ms between data frames;
standard length is a predetermined duration of time in ms; and
Beta is a random variable with a value between 0 and 1.
2. The system of claim 1 , wherein said preamble portion includes an Amplitude Shift Keyed wake up signal.
3. The system of claim 1 , wherein said plurality of data packets are transmitted in Frequency Shift Keyed format.
4. The system of claim 1 , wherein said plurality of data packets include a data preamble including 15 data zero bits and one start bit having a data value of “1”.
5. The system of claim 1 , wherein said plurality of data packets include an identification code.
6. The system of claim 1 , wherein said plurality of data packets includes an identification number including device serial number and product type.
7. The system of claim 1 , wherein said plurality of data packets includes pressure information indicative of pressure within said tire.
8. The system of claim 1 , wherein said plurality of data packets includes temperature information indicative of temperature within said tire.
9. The system of claim 1 , wherein said plurality of data packets include status information indicative of current operational conditions of said sensor.
10. The system of claim 9 , wherein said status information includes information indicative of a low battery condition.
11. The system of claim 1 , wherein said signal indicative of tire conditions is initiated at predetermined intervals.
12. The system of claim 11 , wherein said signal indicative of tire conditions is initiated at intervals shorter than said predetermined intervals in response to a desired rate of change of any conditions monitored within the tire.
13. The system of claim 1 , wherein said time interval between said plurality of data packets is variable.
14. The system of claim 13 , wherein said variable time interval varies between 100 milliseconds and 200 milliseconds.
15. The system of claim 1 , including a check sum data packet including a binary value equivalent to a decimal sum of all data bits.
16. The system of claim 1 , including a low battery bit set to a value of “0” when at battery voltage is within a predetermined range, and set to a value of “1” when out of said predetermined range.
17. The system of claim 2 wherein said wake up portion includes a pattern selected to minimize duty cycle.
18. The system of claim 1 , including four bits indicating specific wake up status codes.
19. The system of claim 18 , wherein said wake up status codes indicates a status of said sensor, said status includes learn, Normal, Over temp, Wake and LF.
20. The system of claim 1 , including transmitting said signal at predetermined intervals in response to movement of the motor vehicle.
21. The system of claim 1 , including increasing the duration between transmissions of signals in response to the motor vehicle decreasing in speed below a predetermined speed.
22. The system of claim 1 , including at receiver for receiving ASK signals and FSK signals.
23. The system of claim 22 , wherein said receiver defaults to receiving ASK signals.
24. The system of claim 22 , wherein said receiver receives ASK signals from a remote keyless entry system.
25. The system of claim 1 , wherein each of said plurality of data packets includes a time interval value indicating when transmission of a subsequent one of said plurality of data packets will occur.