This invention pertains to the art of radio devices and particularly to autonomous power supplies for use therewith.
The invention is particularly applicable to a piezoelectric reed transducer power supply for use in an abnormal tire condition warning system including an electrically powered radio frequency transmitter. Such a power supply may be advantageously employed in conjunction with a low tire warning system as is disclosed in U.S. Pat. No. 4,237,728 as incorporated herein by reference. However, it will be appreciated by those skilled in the art that the invention can be readily adapted for use in other environments as, for example, where similar autonomous or self-contained power supplies are employed to provide electrical energy.
The subject tire condition warning system includes a radio transmitter circuit to be mounted in a pneumatic tire preferrably of the type used on an automobile wherein the tire is mounted on a tire rim and the tire is subject to normal operating vibrations. Such a location is extremely hazardous to the system and will subject it to extreme shock, vibration, temperature and pressure. In addition, the location is relatively inaccessible for regular maintenance and repair. Power supplies for such systems have therefore been required to be able to withstand the harsh environment and yet provide a reliable source of electrical energy over the life span of the tire.
Prior vibrating piezoelectric transducer power supplies have heretofore been suggested and employed. However, such prior power supplies have met with varying degrees of success.
It has been found that acceleration forces in excess of 25 g's may induce damaging types of flexure movement to the transducer. In particular, such damaging flexure movement includes unsafe bending amplitudes which stress the piezoelectric materials of the transducer thereby causing cracking, chipping or breakage of the transducer itself and compound bending flexure movements which similarly produce high and damaging stress levels to the piezoelectric crystal materials. In addition, significant shock inputs to the crystal material from impingement of the transducer against the transducer housing can cause damage.
Another problem inherent in prior vibrating transducer power supplies for use in tire condition warning systems has comprised transducers which were only sensitive to irregular tire vibrations and which would accordingly produce a varying electrical energy output dependent upon tire operation. Such a problem would preclude use of the power supply with a wide variety of wheel sizes and centrifugal loads.
Yet another problem existing in vibrating transducer power supplies included on a rotating item such as a wheel is that when the transducer is off-line from a radiating center line of the rotating item, centrifugal forces will urge the transducer into alignment with the center line. Such urging may inhibit vibrating of the transducer as where alignment of the transducer along the center line will cause it to maintain an abutment with an adjacent wall or support member.
The present invention contemplates a new and improved device which overcomes certain of the above referred to problems and others to provide a new piezoelectric transducer power supply compatible for use in a tire condition warning system which is simple in design, economical to manufacture, readily adaptable to a plurality of uses with a wide variety of tire wheel sizes, radio circuits and centrifugal loads, easy to install and which provides improved operation for the generation of electrical energy.