Method and apparatus for improving the reliability of an airflow measuring system

In an internal combustion engine system having an air intake pipe (38) to induct air thereto and a switching means capable of turning the engine OFF and subject to periodic operation upon operation of the internal combustion engine system, having

• an airflow measuring apparatus having a temperature-dependent resistance element positioned in the path of said airflow, and regulator means connected to said sensing element for controlling current flow through said sensing element in such a manner that said sensing element remains at a substantially contact operating temperature and wherein said sensing element accumulates undesired deposits during the operating life thereof;
• a method for accurately determining air flow through the intake pipe of the engine by preventing the accumulation of said undesired deposits on the resistor,
• comprising the steps of
• periodically commanding a deposit burn-off operation by increasing the current through said sensing element to a predetermined current heating said sensing element to a temperature substantially above said operating temperature, thereby burning off said deposits;
• and controlling the occurrence of the burn-off operation as a function of the periodic operation of the switching means of the internal combustion engine system and while the engine is stopped or OFF.

In an internal combustion engine system having an intake pipe (38) to induct air thereto,

• an air flow measuring apparatus located in the intake pipe of the engine and having a temperature varying resistor (11) positioned in said intake pipe, said temperature varying resistor having a resistance characteristic varying as a function of the quantity of said air flow and a surface subject to accumulation of undesired deposits upon being exposed to said air flow, said air flow measuring apparatus further having regulator means (16) connected to said resistor for furnishing a regulator signal maintaining said temperature varying resistor at a selected temperature, whereby said regulator signal constitutes a measure of said quantity of said air flow,
• a bridge circuit including said temperature varying resistor (11) in at least a portion of an arm thereof;
• a temperature independent resistor (12) in another arm of said bridge circuit and serially connected to said temperature varying resistor (11), the temperature independent resistor being located downstream in the intake pipe (38) with respect to said air flow of said temperature varying resistor (11) for heating air flowing past said temperature dependent resistor in reverse direction and minimize change in resistance of said temperature varying resistor upon the occurrence of reverse flow pulses in said intake pipe during operation of the internal combustion engine.

In an internal combustion system having an air intake pipe (38) to induct air thereto and a switching means (35) subject to periodic operation upon operation of the engine system,

• an airflow measuring apparatus located in the intake pipe of the engine having a temperature-varying resistor (11) forming a sensing element positioned in said intake pipe, said temperature-varying resistor having a resistance characteristic varying as a function of the quantity of said airflow and a surface accumulating undesired deposits upon being exposed to said airflow, said airflow measuring apparatus further having regulator means (16) connected to said sensing element for furnishing a regulator signal maintaining said sensing element at a selected temperature, whereby said regulator signal constitutes a measure of said quantity of said airflow,
• electrical current supply means (32, 31) capable of supplying a current to said temperature-varying resistor for increasing the temperature of said temperature-varying resistor above said selected temperature and to a level sufficient to burn off said undesired deposits;
• means controlled by said switching means upon said periodic operation to connect said current supply means to said temperature varying resistor upon said periodic operation of said switching means;
• wherein said regulator means comprises a controlled current source (25, 26) connected to and supplying said temperature varying resistor (11), and a comparator-and-control amplifier (15) comparing an output signal representative of current flow through said temperature varying resistor with a reference (13, 14, 18);
• and start-up signal generating means (27, 28) connected to said comparator-and-control amplifier (15) and applying a minimum signal thereto for comparison with the reference to permit output to be obtained by said comparator-and-control amplifier and initially control said controlled current source to supply the temperature varying resistor upon start-up of the system.