RF RECEIVER FOR PNEUMATIC TIRE LOW PRESSURE MONITORING AND WARNING SYSTEM

• US 3,806,869 A
• Filed: 09/15/1972
• Issued: 04/23/1974
• Est. Priority Date: 09/15/1972
• Status: Expired due to Term

• Current Assignee: Henry Davis Jr
• Original Assignee: Henry Davis Jr
• Inventors: Davis, Henry Jr.
• Primary Examiner(s): Waring, Alvin H.
• Application Number:
  US05/289,462
• Time in Patent Office: 585 Days
• Field of Search: 340/58 325/15,111,117 200/61.22,61.25,61.26
• US Class Current: 340/447
• CPC Class Codes: B60C 23/0433 Radio signals

Abstract

An improved RF receiver for pneumatic tire low pressure monitoring and warning system is provided which senses a low pressure condition in a pneumatic tire and employs a transmitter which is fixed to a rotatable support for rotation therewith. The transmitter is located off center from the central axis of rotation of the rotatable support and is actuated by sensing means to provide pulse modulated output signals at a radio frequency in response to a low pressure condition in the tire. A receiver is provided for receiving the signals and such receiver operates to improve the character of the output signals while removing undesirable signals and such receiver activates an indicating device in response to a low pressure condition in the pneumatic tire.

Claims

1. In combination with a pneumatic tire low pressure monitoring and warning system having a plurality of selectively actuated transmitters, each carried off center by an associated rotary pneumatic tire support and being rotated therewith at a distance from the central axis of rotation, each of said transmitters generating in response to low pressure within the tire a pulse modulated RF signal within a presselected RF band, said RF signals being pulse modulated with a rate falling within a preselected pulse frequency band;

a plurality of receiving antennas, each respectively attached in a fixed position adjacent an associated rotating transmitter within the near field of and coupled therewith, said coupling being subject to large variations resulting from differences in distance, orientation and shielding, said receiving antennas receiving usable radio frequency signals comprising a train of pulses during each small portion of each complete rotation of an associated transmitter therepast when said coupling is maximized, an RF receiver for the reliable reception and display of recognizable RF signals within a preselected RF band while rejecting the effects of power supply disturbances as well as atmospheric and man-made RF signals not in conformance with the characteristics of the recognizable RF signals, an RF transmission line operatively connecting each antenna with said RF receiver, and indicating means operatively connected with the receiver to provide an indication of low pressure, a power supply for providing voltage controlled and filtered power, said RF receiver comprising a summer receiving the RF signals from said RF transmission lines;

a tunable RF amplifier to provide a first selection of said recognizable signals and amplification to insure efficient amplitude detection;

an amplitude detector for the demodulation of said pulse modulated recognizable RF signals;

an LF amplifier, limiter and filter for making a second selection of said recognizable RF signals by the attenuation of LF signals outside said pulse frequency band;

a rectifier-integrator for said pulse trains to provide a third selection of said recognizable RF signals and to generate a first control signal;

said indicating means providing an inadequate indication when said first control signal is used to control said indicting means directly; and

pulse stretching means for generating a second control signal having pulses with the same pulse repetition rate as the first control signal wherein said effective pulses are of substantially longer duration; and

a power output transistor for energizing said indicating means, said power transistor also comprising an active portion of said pulse stretcher.

2. An RF receiver as set forth in claim 1 in which said summer provides a direct parallel connection of all said RF transmission lines to said RF receiver, and in which said receiver provides increased amplification in the downstream circuitry to compensate for the RF signal power loss due to the mutual loading of said multiple transmission lines.

3. An RF receiver as set forth in claim 2 in which said RF amplifier is comprised of a plurality of shielded RF transformer coupled transistor amplifiers, said RF transformers having magnetic slug tuned primary windings and untuned secondary windings to provide a minimal RF band compatible with the assured inclusion of said entire selected RF band.

4. An RF receiver as set forth in claim 3 in which said amplitude detector comprises a forward biased diode amplitude detector to facilitate its performance at low voltage levels thereby permitting the use of a minimal amount of RF amplication and wherein said diode has its cathode grounded and is housed within the downstream one of said shielded RF transformers to minimize extraneous feedback.

5. An RF rEceiver as set forth in claim 1 in which said LF amplifier, limiter and filter comprise a plurality of capacity coupled transistor amplifiers, wherein the collector loads comprise capacity-inductance tuned tank circuitry thereby defining a minimal LF pass band with the assumed inclusion of the selected pulse repetition frequency band;

and diode connected across the signal path to limit the pulse voltage amplitude.

6. An RF receiver as set forth in claim 5 in which said receiver has a capacity loaded diode rectifier-integrator provided downstream from said LF amplifier, limiter and filter to assure that an effective first control signal is only generated when the output signal from said LF amplifier, limiter and filter comprise at least a minimum number of pulses in said pulse trains.

7. An RF receiver as set forth in claim 6 in which said rectifier-integrator is comprised of a push-pull dual rectifier defined by a pair of cooperative diodes, coupling and storage capacitors and a load resistor to provide a substantially greater pulse peak of the first control voltage and correspondingly higher gain.

8. An RF receiver as set forth in claim 7 in which said indicating means provides an inadequate indication when said first control voltage is used to control the current through said indicating means without altering its waveshape;

and in which said pulse stretching means comprises a power transistor for which the collector load controls said indicating means, said power transistor being normally OFF with its base connected to the output of said rectifier-integrator and, therefore, initially controlled by said first control signal; and

a control transistor which is normally ON, said control transistor having a coupling capacitor connected from the junction of the said indicating means and said power transistor collector to the base of said control transistor with its collector connected to the base of said power transistor;

said coupling capacitor serving to increase the ON time of said power transistor an amount equal to the time required for the said coupling capacitor to discharge, thereby generating a second control signal, which will provide effective pulses of substantially greater duration, to provide a reliable indication.

9. An RF receiver as set forth in claim 8 in which said indicating means is an incandescent filament lamp.

10. An RF receiver as set forth in claim 9 in which operating power is provided by the storage battery of an associated vehicle;

resistance-capacitance filtering means to prevent power supply disturbances from reaching and interfering with the reliable operation of said RF receiver circuitry; and

voltage regulator means for the control of the supply voltage for all circuit elements of said RF receiver with the exception of said power output stage.

11. An RF receiver as set forth in claim 10 in which said voltage regulator comprises a Zener diode.