Area type flow rate measuring device

A device for measuring the flow rate of air drawn into an internal combustion engine, said device comprising:

• (a) an air intake conduit through which air is drawn into the engine;
• (b) throttle valve means positioned in the conduit for controlling the flow rate of air therethrough;
• (c) a sensor valve means positioned in the conduit upstream of the throttle valve means whereby the opening of the throttle valve means produces a difference in pressure across the sensor valve means;
• (d) servo means operable to adjust the sensor valve means such that the pressure differential across the throttle valve means and the sensor valve means remains constant such that the measure of the flow rate of air past the sensor valve means is measured in terms of the area of the opening of the sensor valve means, the servo means including:
• a control valve disposed between first and second control chambers in said servo means,
• a first passage means extending from the conduit upstream of the sensor valve means to the first control chamber and a second passage means extending from said second control chamber to a sensor valve control means,
• a variable flow orifice means between said first and second control chambers wherein the variable flow orifice means varies its opening area in response to any variation of the control valve, thereby varying the pressure in the second control chamber,
• said sensor valve control means being responsive to the pressure in said second control chamber and including means coupled to the sensor valve means for varying the sensor valve means as a function of the air pressure in the second control chamber;
• and a third passage means extending from between said sensor valve means and said throttle valve means and extending to said servo means, said control valve including means responsive to pressure in said third passage means to vary its opening
• (e) a pressure amplifying means including:
• a bypass passage means connected between the upstream and downstream portions of the conduit across the sensor valve means,
• pressure decreasing means connected in the bypass pipeline for decreasing the pressure of air flowing therethrough, and a fourth passage means from said bypass passage means to said second control chamber and in communication with the decreased pressure from said pressure decreasing means
• whereby the pressure difference across the sensor valve means is amplified in the second control chamber by the pressure amplifying means such that the air pressure in the control chamber has a magnitude of variation sufficient to ensure reliable operation of the sensor valve means.