Two stage flowmeter

• Main Authors: OLSON; JERRY A, MIGRIN; ROBERT S
• Format: Patent
• Language: English
• Published: 11.11.1980
• Subjects: MEASURING; MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUIDLEVEL; METERING BY VOLUME; PHYSICS; TESTING

A low pressure drop air flowmeter for an automobile engine is disclosed. The meter contains a main air flow passage, a relatively small venturi to receive a portion of the air flow, pressure ports for sensing stagnation and static pressure and a set of swirl vanes disposed adjacent the outlet of the venturi and operative to impart a swirl to the remainder of the air in the main passage, thereby creating a reduced pressure at the venturi outlet for amplifying the pressure difference between the stagnation and static pressure without appreciably increasing the pressure drop across the flowmeter. A tertiary passage provides a path of fluid communication between points upstream and downstream of the swirl vanes. This passage can be selectively opened or restricted by a valve which, in the preferred embodiment of the invention, opens the tertiary passage with increasing overall flow rate. This arrangement results in a fluid flowmeter having a characteristic pressure drop which is less than that of a conventional device, particularly at high flow rates. Also disclosed is a solenoid valve operative to selectively sample stagnation pressure in the tertiary passage and signal pressure in the throat of the venturi and generate an electrical output signal as a function of the difference between these two pressure signals.