Communications: electrical – Land vehicle alarms or indicators – Internal alarm or indicator responsive to a condition of the...
Reexamination Certificate
2002-02-22
2004-12-07
Hofsass, Jeffery (Department: 2632)
Communications: electrical
Land vehicle alarms or indicators
Internal alarm or indicator responsive to a condition of the...
C340S442000, C340S572100, C340S572700, C073S146500
Reexamination Certificate
active
06828905
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a system having the features specified in the preamble of claim
1
. A device of that kind is known from WO 93/08035. The device comprises a wheel-mounted electronic unit which is located within the pneumatic tyre and exposed to the pressure prevailing in the pneumatic tyre. The wheel-mounted electronic unit comprises a battery as current source, a pressure sensor for measuring the pressure prevailing in the pneumatic tyre, an electronic evaluation circuit for evaluating the measured-pressure signals supplied by the pressure sensor, and a sensor that is controlled by the evaluation circuit and by which signals containing information on the pressure in the tyre, derived from the measurement, are transmitted to a receiver unit. The pressure sensor is a semiconductor-based absolute-pressure sensor and supplies an electric output signal corresponding to the respective current tyre pressure. The receiver unit is a detached remote-control unit containing an interrogator by means of which the wheel-mounted electronic unit can be transferred from a current-saving state, in which a receiving means contained in the wheel-mounted electronic unit and an activation unit are kept in a standby state, into its normal operating state. The wheel-mounted electronic unit then measures the pressure and sends out a signal, containing information on the absolute pressure, to the remote control unit, which latter is provided with a liquid-crystal display from which the measured value can be read. A sequencing control takes care of the timely transmission of the pressure signal. The wheel-mounted electronic unit is then returned to its current-saving state, in which it consumes some microamperes of current. A lithium battery with the dimensions of a button cell, having a nominal voltage of approximately 3 V and a capacity of approximately 50 mAh, permits in this way the tyre pressure to be transmitted approximately 200 times only. If a service life of five years is to be achieved, then the pressure can be interrogated once a week only. This is absolutely insufficient, judging by the requirements of the automobile industry. On the one hand, it is desired for the battery to have a service life commensurate with the service life of the vehicle, because exchanging the battery in the wheel-mounted electronic unit is possible either not at all or only at high cost. On the other hand, effective monitoring of the tyre pressure is not possible with an interrogation frequency as low as once per week. A dangerous situation may arise for the driver when a sudden pressure loss occurs which can be detected only if the tyre pressure is measured at intervals of a few seconds. In order for this to be achieved, advanced tyre pressure monitoring systems do not transmit the tyre pressure every time it is measured, but transmit it only when a pressure deviation that may impair the driving safety becomes apparent or, from time to time, when the serviceability of the wheel-mounted electronic unit is internally checked and reported to the receiver unit. (DE 195 22 486 C2; the AMI DODUCO company publication entitled “Electronic tyre pressure control system. Higher driving safety—higher comfort”). This requires that the pressure be not only measured, but also evaluated in the wheel-mounted electronic unit, for which purpose the wheel-mounted electronic unit comprises an evaluation circuit that controls the transmitter of the tyre pressure electronics and causes it to transmit a signal only if necessary, namely when a relevant pressure deviation has been determined or when the serviceability of the wheel-mounted electronic unit is to be reported. AMI DOCUCO GmbH have succeeded in this way, by strictly optimising the operation of the battery-operated wheel-mounted electronic unit, to reduce the latter's current consumption so effectively that in the meantime the service life of a battery with a charging capacity of 300 mAh is at least seven years, although the wheel-mounted electronic unit measures the pressure every 3 s and transmits a signal every 54 s. The limited service life of the battery nevertheless remained a basic handicap of that tyre pressure monitoring system.
There have been plenty attempts to overcome the dependency of a tyre pressure monitoring system on the service life of a battery in the wheel-mounted electronic unit. There have been suggestions to equip the wheel-mounted electronic unit with mechanoelectric or thermoelectric transducers which would derive energy from the flexing work of the tyre during motion or from the heat developed during this process, convert such energy into electric current and use the latter to feed an accumulator for the operation of the wheel-mounted electronic unit. Such solutions are, however, too costly and do not offer the required reliability and service life under the rough operating conditions in driving operation.
Another suggestion proposes to supply the required energy to the wheel-mounted electronic unit from the outside, by means of a transponder. The current consumption of the wheel-mounted electronic unit is predominantly not due to measuring and transmitting processes, but to the pauses between the measuring processes when the wheel-mounted electronic unit must be kept in a standby state and when an internal clock operates. A tyre pressure monitoring system of this kind is described in the Internet by the SSI company; the website can be visited under. A transponder, or a responder, is a radio system that operates without a current supply of its own, transmits answering signals in response to interrogation signals received, and derives the energy required for this purpose from the very interrogation signals. In the case of the tyre pressure monitoring system, an interrogator, transmitting the interrogation signals, and a responder, receiving the answering signals transmitted by the transponder, are provided in the vehicle for this purpose. The tyre pressure monitoring system from SSI has the interrogator and the responder combined in one transmitter/receiver unit, which in the case of a vehicle with four wheels is connected to four antennas arranged in the wheel wells of the body close to the wheels. The interrogator sends out at regular time intervals an interrogation signal to a transponder included in the wheel-mounted electronic unit, and the transponder activates the wheel-mounted electronic unit, which contains neither a battery nor an accumulator, and transmits to it simultaneously the electric energy required by it to carry out a measuring operation and to transmit the measuring result back to the responder. It is a disadvantage of this system that the wheel-mounted electronic unit with the transponder is arranged, well-shielded, inside the wheel. The wheel rim, a steel belt in the tyre and fillers in the rubber of the tyre attenuate the signals transmitted by the interrogator and by the transponder so heavily that the antennas of the interrogator and of the responder must be arranged in close proximity to each wheel and the power of the interrogator must be sufficiently high to activate the wheel-mounted electronic unit and to make available, in addition, sufficient transmitting power for re-transmitting a tyre pressure signal. This makes that solution so expensive that it has not till now found acceptance in practice.
SUMMARY OF THE INVENTION
Now, it is the object of the present invention to open up a way of further increasing the service life of the battery in a battery-operated wheel-mounted electronic unit of a tyre pressure monitoring system without having to reduce the measuring rate for the tyre pressure.
This object is achieved by a system having the features set forth in claim
1
. Advantageous further developments of the invention are the subject of the dependent Claims.
The invention combines a system of the known species, which is dependant on a battery, in a non-obvious manner with elements of the system that instead of using a battery works with a transponder, thereby achieving a
Kessler Ralf
Kühnle Andreas
Normann Norbert
Schulze Gunter Lothar
Hofsass Jeffery
Pham Lam
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