Abstract: The trailer hitch alignment system of the present invention includes an alerting device and a tow bar assembly for attachment to a towing vehicle. The tow bar assembly includes a photoelectric sensor for detecting the vertical alignment of a trailer tongue. The tow bar assembly has a hitch ball with a spherical top and a cylindrical body for coupling with a trailer tongue having a semi-spherical socket. In one embodiment, the photoelectric sensor is mounted on the tow bar of the tow bar assembly, adjacent to the hitch ball. In another embodiment, the hitch ball houses the photoelectric sensor within its interior. During operation, the driver of the towing vehicle typically maneuvers the vehicle toward the trailer in a rearward direction. Once the photoelectric sensor detects the vertical alignment of the socket with the ball, the alerting device is activated informing the driver of the alignment.

Abstract: The changer includes a filter supporting frame attached to a supply spool containing fresh filter material and a take-up spool for storing the clogged filter material. The frame is substantially rectangular in shape and has attached thereto a sensor switch which is disposed medially of the frame and the filter material disposed thereacross. The switch is actuated when the filter material becomes clogged to a point where deflection of the material in response to circulating air flow occurs. The switch actuates a drive motor attached to the take-up spool causing the take-up spool to wind the clogged material thereon thereby replacing it with clean filter material from the supply spool. The filter material itself contains transverse enlarged linear elements which are longitudinally spaced along the filter material at intervals equivalent to the width of the frame. The enlarged areas actuate a switch which causes cessation of the motor drive, thereby insuring accurate placement of the fresh filter material.