Air flow measuring device for internal combustion engines

A device for measuring the mass rate of flow of a gas flowing in a channel comprising a flow detection valve positioned in the channel, a feedback control mechanism operatively associated with said flow detection valve, said mechanism comprising a pressure-sensitive amplifier unit and a valve actuating unit, said feedback control unit being operable to maintain constant the pressure difference across the flow detection valve so that the degree of opening of the flow detection valve is made proportional to the amount of the gas past the same valve, said pressure-sensitive amplifier unit having a variable-area orifice which is under the control of a pressure difference setting diaphragm for producing an actuating pressure which actuates the valve actuating means operatively connected to the flow detection valve so that the pressure difference is maintained at a predetermined value, a chamber connected to a portion of the channel downstream of the detection valve through a first conduit and a chamber isolated from the first said chamber by the pressure difference setting diaphragm and connected to a portion of the channel upstream of the detection valve through a second conduit, a valve body constituting the variable-area orifice connected to the pressure difference setting diaphragm which is acted on by a compensation mechanism so as to compensate for variations in the specific gravity of the gas flowing in the channel owing to pressure and temperature variations, the compensation mechanism comprising a bellows located in a chamber conducting the gas flowing in the channel, said bellows being filled with a given mass of a certain gas in such a manner that when the gas being measured and surrounding the bellows is at its reference temperature, the gas pressure in the bellows becomes equal to a reference pressure of the gas being measured, and that the product of the effective pressure-sensitive area of the pressure difference setting diaphragm and the pressure difference across the detection valve is equal to the product of the effective pressure-sensitive area of the bellows and the gas pressure in the bellows, in which device said bellows is operatively connected to the pressure difference setting diaphragm of the amplifier means so that a force produced by said bellows acts as a mechanical counterforce to push against a force produced by the diaphragm due to the pressure difference, and in which device a pressure difference setting spring cooperates with the bellows, said spring being so located that a force produced by the bellows in response to alteration in temperature and pressure of the gas flowing in the channel and a force of said spring operate upon the pressure difference setting diaphragm in parallel with each other.

In an internal combustion engine having a fuel control unit, air suction pipe means and pedal accelerator means, the improvement of a suction air flow measuring device of the weight-rate of flow type, said measuring device comprising an upstream valve positioned in the air suction pipe means, a downstream valve positioned in the air suction pipe means and in series downstream from said upstream valve, one of the said upstream valve and the downstream valve serving as a flow detection valve with the remaining valve serving as a flow regulating valve, one of the said upstream valve and said downstream valve defining an area flowmeter for determining the amount of incoming air flow on the basis of the opening area of the valve serving as the flow detection valve by keeping the difference in the pressure existing on opposite sides of the valve serving as the flow detection valve constant;

• pressure-sensitive amplifier means operatively associated with said defined area flowmeter, said amplifier means including a pressure difference setting diaphragm means for detecting and amplifying the deviation of the pressure difference that may occur in the defined area flowmeter, a valve opening means operatively associated on one side with said pressure sensitive amplifier means and on the other side with one of the upstream valve and the downstream valve functioning as the flow detection valve for controlling the opening and closing of the flow detection valve by the output from the pressure-sensitive amplifier means, said pressure-sensitive amplifier means and said valve opening means defining a flow servomechanism, the one of the upstream valve and the downstream valve serving as the flow detection valve being operatively connected to the fuel control unit with the other of the valves serving as the flow regulating valve being operatively connected to the pedal accelerator means;
• and gas-filled bellows means operatively connected to the pressure difference setting diaphragm of said amplifier means so that a force produced by said bellows means acts as a mechanical counterforce to push against a force produced by the diaphragm due to the pressure difference, whereby said association of said defined area flowmeter, said defined flow servomechanism, and said bellows means will be such that the product of the effective pressure-sensitive area of said pressure difference setting diaphragm of said pressure-sensitive amplifier means and a reference pressure-difference is equal to the product of a reference pressure of the gas enclosed in said bellows means and the effective pressure-sensitive area of said bellows means.