Abstract: Each time clogging of a filter (5) of an air cleaner is determined on the basis of intake negative pressure of an engine (2), and the air filter (5) is cleaned, an accumulated value of operating time of the engine (2) from previous cleaning until clogging is determined is taken as a cleaning interval (S), and sequentially measured. A plurality of stages are previously set by classifying a minimum value and a maximum value of the cleaning interval (S), and the measured cleaning interval (S) is added to the stage to which the measured cleaning interval (S) is to belong, among the stages. A histogram in which an axis of abscissas is taken as the stage, an axis of ordinates is taken as frequency of the cleaning interval (S) is constructed, and an approximate straight line (L2) illustrated by a solid line is obtained by approximating a characteristic line (L1) of the histogram illustrated by a dotted line to a straight line.

Abstract: A rotary machine, in particular electric motor, includes a position sensing means for sensing a rotational position of a pole wheel that is rotatable about an axis of rotation. The pole wheel has a circumferential edge, and the position sensing means has at least one first position sensor for sensing a change in a magnetic field, at least one magnetic element arranged on the pole wheel, and at least one circuit card on which electronic components are arranged. The first position sensor is arranged at least indirectly on the circuit card. The first position sensor extends at least partially into a space of the pole wheel that surrounded by the circumferential edge.

Abstract: In some examples, a device comprises a substrate including a notch formed in a surface of the substrate and a semiconductor die positioned in the notch and including an electrochemical sensor on an active surface of the semiconductor die. The device also comprises a chemically inert member abutting the surface of the substrate and including an orifice in vertical alignment with the electrochemical sensor as a result of the semiconductor die being positioned in the notch. The device also comprises a compressed o-ring seal positioned between the chemically inert member and the active surface of the semiconductor die, the compressed o-ring seal circumscribing the electrochemical sensor.

Abstract: The present invention provides a novel combination of devices to measure and transmit to an electronic controller data pertaining to differential pressures, temperatures, regeneration status, exhaust content, accumulated gas consumption and substitute fuel consumption. The electronic controller compares the data to thresholds; when the controller receives signals indicating these thresholds or limits are met, the controller causes the gas substitution rate to be diminished or set to zero until after-treatments elements are fully regenerated thereby facilitating integration of a mixed fuel system with an application internal combustion engine.

Abstract: A valve used in combination with a vessel containing fluid in the interior and a parameter measuring device. The valve allows the device to be exposed to the fluid in the interior of the vessel. The device may be installed into the valve, and the valve may be fitted to the side of the vessel. The valve improves upon other prior art by providing provisions for purging air trapped in the internal cavity of the valve. The valve includes a purge position, which provides a smaller opening from the interior of the vessel to the internal cavity and an air path to the external atmosphere. Fluid may fill the valve pushing trapped air out of the valve until the majority of the trapped air is expelled.

Abstract: A data processing method of variable measurement data in an electronic control unit (ECU) is provided. The ECU that processes the data processing method calculates a filtering frequency based on a delay time frequency based on a transmission timing cycle of the measurement data and a processing timing cycle of the measurement data in the ECU, and also based on a pulsation frequency of the measurement data, and removes, from the measurement data, a component of the filtering frequency calculated in the calculation of the filtering frequency.

Abstract: A method of determining an operational status of an exhaust gas recirculation valve of an internal combustion engine arrangement, the EGR valve being configured to control a flow of combusted exhaust gas from an exhaust manifold to an inlet manifold of the ICE arrangement. The method comprising controlling the EGR valve to transition from a closed position; obtaining a signal indicative of a variation of temperature level of the gas present in the inlet manifold at a duration between a first point in time and a second point in time when the EGR valve assumes the open position; determining, based on the signal indicative of the variation of the temperature level, a velocity value indicative of a maximum increase in change of temperature level during the time period between the first point in time and the second point in time; comparing the velocity value with a predetermined threshold; and determining that the EGR valve is operational when the velocity value is higher than the predetermined threshold.

Abstract: An automatic mounting and demounting device and system for a motor testing platform, adapted to enable a control host to control automatic mounting and demounting between an axle of a motor under test and an axle of a testing apparatus, includes a mobile platform and a positional information sensing member. The control host controls the mobile platform according to positional information generated by the positional information sensing member, such that a carrier for carrying the motor under test is automatically driven to a corresponding position to thereby effect alignment and connection or separation of the axle of the motor under test and the axle of the testing apparatus. Therefore, preparation for the motor dynamics testing is automatically carried out effectively and correctly, thereby reducing the time and manpower required for testing-related preparation.

Abstract: Systems and methods for determining degradation of a cylinder deactivation mechanism are described. In one example, engine data generated while an engine is operation with all of its cylinders active is used to correct engine data generated while one or more engine cylinders are deactivated to improve detection of a degraded cylinder deactivation mechanism.

Abstract: An internal combustion engine includes an engine block, a combustion cylinder including a cylinder wall, engine oil and engine coolant. Control of the internal combustion engine includes estimating the cylinder wall temperature in a temperature state estimator, comparing the estimated cylinder wall temperature to a predetermined temperature threshold, and circulating the engine coolant in the engine when the estimated cylinder wall temperature exceeds the predetermined temperature threshold.

Abstract: Disclosed is a method for detecting the clogging of an air filter including the following steps when the cross section for the passage of air in an intake tract is greater than a predetermined passage cross section: measuring a pressure in the intake tract at the end of a phase of admitting air into a cylinder; measuring a pressure in the intake tract at the end of an exhaust phase in a cylinder; and determining that the air filter is clogged by comparison between at least one pressure measured during a pressure measurement at the end of the phase of admitting air into a cylinder and, on the other hand, a pressure measured during a pressure measurement at the end of the exhaust phase, the filter being estimated to be clogged when the comparison yields a value higher than a predetermined value.

Abstract: A diagnostic apparatus for an evaporative fuel processing system includes a fuel tank retaining fuel to be fed to a pressure-charger-equipped engine, a canister communicating with the fuel tank and adsorbing evaporative fuel generated therein, an upstream purge line allowing the canister and an engine intake system to communicate at an upstream side of the pressure charger, an upstream purge valve that opens and closes the upstream purge line, a pressure detector detecting pressure in the upstream purge line; a valve controller that opens and closes the upstream purge valve during pressure-charging and non-pressure-charging, respectively, a first timekeeper measuring an accumulative time in which a diagnosis execution condition is satisfied after a purge-flow diagnosis is started, and a determiner determining that the system operates normally or abnormally depending on whether the pressure decreases or not by a predetermined pressure or more from the start of the diagnosis.

Abstract: An internal combustion engine includes an exhaust pipe having an interior through which exhaust gas flows, a pressure delivery pipe connected to the exhaust pipe, an interior of the pressure delivery pipe communicating with the interior of the exhaust pipe, a pressure sensor connected to the pressure delivery pipe, the pressure sensor detecting a pressure of the interior of the exhaust pipe, and a fastener that fixes the pressure delivery pipe to the exhaust pipe. A part of the fastener is exposed in the interior of the exhaust pipe.

Abstract: A sensor arrangement of an internal combustion engine includes an intake duct including one or more curved parts bent or curved and connecting an intercooler and a throttle; and a pressure sensor provided on the intake duct and configured to detect a pressure in the intake duct. The pressure sensor includes a detector disposed close to an outside curved portion of a curved part.

Abstract: Systems and methods for determining operation of a cylinder deactivating/reactivating device are disclosed. In one example, a warm engine is rotated without being supplied fuel to determine the presence or absence of valve actuator degradation. Degraded valve actuators may be determined when there is a lack of a temperature rise in the engine exhaust system.

Abstract: A portable vacuum pressure graphing gauge device enabling users of vacuum systems the ability to see trends of vacuum systems through real time plotting of a pressure vs. time curve on a hand held instrument, enabling them to understand what is going on in their system, or the like. A device may include several graphical modes designed to even more easily interpret vacuum data, and packaging that is rugged and versatile including a magnet, kickstand, wireless connectivity, visual and audible set points, automatic sensor fault detection, and several vacuum pressure measurement units to choose from, or the like.

Abstract: An electronic control unit diagnoses leakage abnormality in an intake system downstream from a supercharger provided in the intake system of the engine. The electronic control unit sets, as a supercharging region monitoring value, a ratio between a first air amount obtained from a detection value of an air flowmeter and a second air amount obtained from a detection value of an intake pressure sensor, the ratio being the ratio obtained when the engine is operated in a supercharging region. The electronic control unit also sets, as a non-supercharging region monitoring value, a ratio obtained when the engine is driven in a non-supercharging region. The electronic control unit determines the presence of the leakage abnormality in the intake system when the ratio of the supercharging region monitoring value to the non-supercharging region monitoring value is larger than a predetermined specified value.

Abstract: A method is provided for identifying an averaged sensor value of a state variable of an air system for an internal combustion engine in a motor vehicle, comprising the following steps: acquiring and temporarily storing sensor values at a predefined sampling interval during a segment duration of the state variable, the segment duration corresponding to one period of a pulsation of the state variable; determining an average of the sensor values acquired within the segment duration; correcting the average of the sensor values that has been determined, using a correction variable that depends on the time difference between the segment duration and a multiple of the sampling interval.

Abstract: An anomaly determination system includes inlet and outlet pressure sensors for a pressure loss portion, an outside pressure sensor, and an anomaly determination section for determining an anomaly of the pressure loss portion. The anomaly determination section determines that the pressure loss portion is anomalous if the following two conditions are both met: a difference between the inlet pressure and the outlet pressure, a difference between the outlet pressure and the outside pressure, and a difference between the outside pressure and the inlet pressure which differences are detected when the flow rate is less than the minimum flow rate are all included in an allowable range; and a pressure difference between the inlet pressure and the outlet pressure when the flow rate is greater than or equal to the minimum flow rate is included in the first pressure loss range.

Abstract: Methods and systems are provided for turbocharger speed control in an engine system having multiple staged charge boosting devices. In one example, compressed air is provided by a turbocharger compressor until a turbocharger speed reaches a limit. Thereafter, a compressor of a downstream supercharger is operated to share the load.

Abstract: Systems, apparatus, and methods are disclosed for diverting a portion of intake airflow from a pressure source in an internal combustion engine system. The intake airflow is diverted to, for example, an air compressor at the intake of the pressure source before the airflow is pressurized by the pressure source.

Abstract: A vehicle sound generation apparatus 20 is constituted by a first pressure sensor 21a, a second pressure sensor 21b, a signal processing section 24 which performs processing of changing pressure signals output from the first pressure sensor 21a and the second pressure sensor 21b in accordance with the operation state of an automobile 10, and speakers 28a, 28b which output, as an intake sound of an engine 12, a sound pressure signal processed by the signal processing section 24. The first pressure sensor 21a is provided on an intake duct 15 connecting an air cleaner 16 and a throttle body 17 at a position between the air cleaner 16 and the center of the intake duct 15, and the second pressure sensor 21b is provided between the engine 12 and the throttle body 17.

Abstract: A supercharging system includes a waste gate valve (35) mounted in a bypass passage (34) that bypasses a turbine (31) and through which exhaust gas flows. An electronic control unit (39) that diagnoses abnormality of the supercharging system makes a first abnormality determination and a second abnormality determination, each of which is based on an integrated value of an intake air amount and an increased amount of supercharging pressure in each of a first determination period from initiation to termination of an increase in the supercharging pressure and a second determination period from initiation to termination of an increase in the intake air amount.

Abstract: A method for operating a hybrid vehicle and a hybrid vehicle are disclosed. The hybrid vehicle includes a supercharged internal combustion engine having an overboost function and at least one electric drive. An overboost phase of the supercharger of the internal combustion engine is followed by a regeneration phase of the supercharger and a corresponding drop in torque, wherein the at least one electric drive is used to at least partially compensate for the drop in torque of the internal combustion engine during the overboost regeneration phase of the supercharger. Thus, an improved driving behavior with an extended overboost phase can be achieved.

Abstract: In a pressure detection device which is provided in an intake pressure measurement apparatus, a detection space surrounded by an outer wall portion is formed in a housing, and an inner wall portion is formed integrally in the detection space such that both end portions are connected to the outer wall portion. The inner wall portion has a cylindrical shape, and a sensor storage portion is formed between the inner wall portion and the outer wall portion. In the sensor storage portion, a pressure sensor is disposed in a region with the least influence of thermal stress at a position closer to the inner wall portion than the outer wall portion.

Abstract: A method for checking the functioning of a ventilation apparatus for ventilating a crankcase connected via the ventilation apparatus to an air supply system of the internal combustion engine includes: determining a pressure difference between an ambient pressure and a crankcase pressure in the crankcase; identifying a fault in the ventilating apparatus as a function of the pressure difference if an enabling condition is met; the enabling condition being met if an air mass flow in the air supply system, filtered by a low-pass filter, exceeds a first threshold value in terms of absolute value.

Abstract: A method for diagnosing an actuator for a boost pressure system of an internal combustion engine, in which the actuator is controlled using a triggering signal, and a state variable of the boost pressure system which is at least an indirect function of the triggering signal is detected. The triggering signal is periodic, and a curve of the values of the state variable is analyzed with regard to at least one periodic characteristic.

Abstract: An end-of-life estimation device for an air cleaner, which is capable of always accurately estimating an end of a service life of the air cleaner with an inexpensive construction, thereby enabling the air cleaner to be efficiently used until the service life comes close to the end. The end-of-life estimation device calculates a life parameter indicative of remaining service life of the air cleaner during running of an engine, on an as needed basis, and stores a relationship between the degree of clogging of the air cleaner, an intake air amount, and an intake parameter (an intake pressure on a downstream side of the air cleaner and/or a throttle valve opening). Further, the end-of-life estimation device calculates and updates a reference value with reference to which the life parameter is calculated, based on the stored relationship, according to the detected intake air amount and intake parameter.

Abstract: A sensor assembly for use in a vehicle. The sensor assembly has a housing for receiving a substrate. Terminals with substrate mating portions are provided in the housing. The substrate has components mounted thereon and plated openings which extend therethrough. The plated openings are provided in electrical engagement with the terminals. The openings are provided to mechanically and electrically engage the resilient contact portions of the terminals. The substrate mating portions are releasably pressure fit within the plated openings to allow the substrate to be removed and replaced as needed. The substrate mating portions maintain the electrical and mechanical connection between the substrate mating portions and the plated openings when the sensor assembly is exposed to vibration.

Abstract: Methods and systems are provided for using a crankcase vent tube pressure or flow sensor for diagnosing a location and nature of crankcase system integrity breach. The same sensor can also be used for diagnosing air filter plugging and PCV valve degradation. Use of an existing sensor to diagnose multiple engine components provides cost reduction and sensor compaction benefits.

Abstract: An engine testing device for dynamic pressure loss and valve seal-tightness testing of a running four-stroke engine includes: a first pressure gauge detecting a pressure value in an air intake line to a cylinder of the engine and outputting a first output signal indicative of the pressure value detected; a second pressure gauge detecting a pressure value in an exhaust line of the engine and outputting a second output signal indicative of the pressure value detected; a trigger device detecting an electrical signal indicative of when a selected cylinder of the engine is the particular active cylinder; and a measured value detection device detecting the output signals of the first and second pressure gauges and an output signal of the trigger device, such that an association between points in time of the pressure measurements and the particular active cylinder is enabled.

Abstract: A method for detecting leaks within a vacuum system is described. The method may detect vacuum system leaks responsive to vacuum pump speed. The method can compensate for changes in barometric pressure so that a single leak threshold may be provided for all altitudes and barometric pressures.

Abstract: A time-course change (dM/dt) in the mass of air in an intake passage downstream of a throttle value is estimated through application of a mass conservation law to the air in the passage. A time-course change dTm/dt in the temperature of the air in the passage is estimated through application of an energy conservation law to the air in the passage. The pressure of the air in the passage is estimated on the basis of the mass of the air in the passage obtained through integration of dM/dt with respect to time, the intake air temperature obtained through integration of dTm/dt with respect to time, and a state equation applied to the air in the passage. Only the state equation includes a term regarding the volume of the passage. Therefore, it is possible to easily identify the volume while monitoring only a change in the intake air pressure.

Abstract: Disclosed are methods and systems for monitoring and indicating the optimal replacement interval for a filter. In particular, the methods and systems may be utilized for monitoring and indicating the optimal replacement interval of an air filter in an internal combustion engine based on parameters that include air filter plugging rate data, engine duty cycle data, pressure drop across the air filter, penalty on fuel consumption, and the cost of air filter replacement.

Abstract: The invention relates to a method for estimating the temperature of a gas pressure sensor attached to a wall of a turbocharged motor vehicle diesel engine, said sensor being positioned upstream of the turbine of the turbocharger. According to the invention, the temperature of the gas pressure sensor is estimated at least by measuring the temperature of the external air and the temperature of the wall to which the sensor is attached.

Abstract: A method of valve lift failure detection may include determining first and second intake air pressures in an engine having intake valve lifters that selectively operate intake valves in first and second lift modes. The first intake air pressure may correspond to an intake stroke of a first piston of the engine when the engine is commanded to operate in the first lift mode and the second intake air pressure may correspond to an intake stroke of a second piston of the engine when the engine is commanded to operate in the first lift mode. The method may further include determining a difference between the first and second intake air pressures and diagnosing an intake valve lifter failure when the difference exceeds a predetermined limit.

Abstract: A sensor assembly for use in a vehicle. The sensor assembly has a housing for receiving a substrate. Terminals with substrate mating portions are provided in the housing. The substrate has components mounted thereon and plated openings which extend therethrough. The plated openings are provided in electrical engagement with the terminals. The openings are provided to mechanically and electrically engage the resilient contact portions of the terminals. The substrate mating portions are releasably pressure fit within the plated openings to allow the substrate to be removed and replaced as needed. The substrate mating portions maintain the electrical and mechanical connection between the substrate mating portions and the plated openings when the sensor assembly is exposed to vibration.

Abstract: Various methods and systems are provided for a turbocharger. In one example, a method includes determining a first pressure at a first location within a turbocharger and determining a second pressure at a second location within the turbocharger. The method further includes indicating degradation of the turbocharger based on the first pressure and the second pressure.

Abstract: A pressure measurement system includes a multiplexer unit which inputs a plurality of electrical signals representative of pressures, and a comparison unit which compares the electrical signals among each other to determine a specified signal characteristic, wherein the multiplexer unit selects one of the electrical signals as an output signal based on the determination of the specified signal characteristic, and outputs the selected signal.

Abstract: An engine control module having an environmentally-sealed housing includes a housing-mounted air pressure sensor for providing a reliable measure of atmospheric air pressure to a control circuit mounted within the housing. The sensor is mounted on an inboard face of the housing, and includes a sensor element, a body portion and a riser portion. The sensor element is mounted in the body portion, and the riser portion protrudes through an opening in the housing to couple the sensor element to atmospheric pressure outside the housing. The body portion is sealingly secured to the inboard face of the housing, and a set of conductor pins molded into the body portion extend inward to engage a circuit board enclosed by the housing, and thereby directly couple the sensor element to the ECM's control circuit. The top of the riser portion is capped by a splash-proof lid to prevent water intrusion.

Abstract: A waterproof connecting structure for a pipe for connecting an intake passage of an internal combustion engine and an external gas detector to convey gas into the intake passage. The structure includes a connecting space to which the pipe is connected and a partition wall formed between the intake passage and the connecting space. The connecting space has a larger diameter than the pipe. The partition wall includes an elongate hole for placing the interior of the intake passage and the connecting space in fluid communication. This configuration prevents intrusion of droplets drifting in through intake air and allows a high degree of freedom for location of the pipe.

Abstract: An internal combustion engine has an intake system (1) and an exhaust gas system (4). An exhaust turbocharger of the internal combustion engine has a compressor (42) arranged in the intake system (1) and a turbine (48) arranged in the exhaust gas system (4) of the internal combustion engine for driving the compressor (42). In order to diagnose the intake system (1), a charge pressure (PHS_AIC_DOWN) of the compressor (42) is determined in a predetermined operating state of the internal combustion engine. A leakage of the intake system (1) downstream of the compressor (42) is recognized if the determined charge pressure (PHS_AIC_DOWN) is lower than the predetermined base charge pressure (PUT_BAS) in the predetermined operating state.

Abstract: A method of determining opening of an intake valve of an internal combustion engine, the method including the steps of: determining the time pattern of an intake pressure in an intake manifold of the internal combustion engine, the time pattern of the rotation speed of a drive shaft of the internal combustion engine, or the time pattern of a voltage at the terminals of a battery of the internal combustion engine; determining an intake-frequency component of the intake pressure, the rotation speed, or the voltage; and determining opening of the intake valve as a function of the intake-frequency component of the intake pressure, and also as a function of the intake-frequency component of the rotation speed or voltage.

Abstract: A restriction diagnostic system for a vehicle comprises a pressure difference module and a diagnostic module. The pressure difference module determines a pressure difference between an ambient air pressure and a filtered air pressure measured at a location between an air filter and a valve that is selectively opened to enable ambient airflow through the air filter to a fuel vapor canister. The diagnostic module selectively diagnoses restriction of the airflow through the air filter when the pressure difference is greater than a predetermined pressure.

Abstract: A supercharged internal combustion engine in a motor vehicle includes a venting device for the crankcase of the internal combustion engine and a compressor for supercharging the internal combustion engine. A discharge opening for discharging the crankcase gas is provided upstream of the compressor and a sensor for determining the charge pressure of the compressor is provided downstream of the compressor. The discharge opening is connected to the crankcase by a first connection for the airflow, in particular a hose connection. In order to cost-effectively monitor the venting of the crankcase of the internal combustion engine, an opening, to which the charge pressure of the compressor is applied, is provided downstream of the compressor. The first connection for the airflow includes a closing device for closing the opening to which the charge pressure is applied, wherein the closing device closes the opening if the first connection is connected to the discharge opening.

Abstract: The present invention utilizes self-heating of electronic components to improve a humidity sensing part with low environment resistance, such as a condensation problem and the like, and also to enhance the heat radiation efficiency of electronic components. The humidity sensing part is used in an intake tube of an automobile by integrating, for example, with a heating resister type mass air flow measurement device. A humidity sensing element is mounted on an electronic circuit board in a mass air flow measurement device with the temperature thereof starting to increase immediately after a sensor has been actuated. This urges the temperature of the humidity sensing element to start increasing (being heated) immediately after the sensor has been actuated. To urge the humidity sensing element to be further heated, a base plate is composed of two types of materials, resin and metal.

Abstract: The present invention provides apparatus (100) and methods for testing for leaks in forced-induction internal combustion engine (10) air intake systems. The apparatus (100) includes a plurality of work faces (132n) each having at least one flange (134n) disposed thereon for attaching the apparatus (100) to an air intake system of an engine (10). An air flow valve (136n) is disposed on each work face (132n), those valves (136n) being moveable between open and closed positions. The apparatus (100) also includes a compressed air supply inlet (138) configured to supply compressed air to the air flow valves (136n). Wherein, compressed air can be supplied to the air intake system of engine (10), via an open valve (136n) which is, in use, internal of the intake system, enabling a simulated air pressure test to be performed in order to locate possible intake system leaks.

Abstract: An engine intake system is provided that includes a sensor unit (16) formed by mounting a throttle sensor (18) and a negative pressure sensor (20) on a sensor housing (17) mounted on a mounting face (15) on one side of a throttle body (1), and a negative pressure transmission path (35) providing communication between an intake path (2) and the negative pressure sensor (20) is formed in a crank shape from a first passage (35a) having one end opening on a peripheral face of an upper half of the intake path (2) in proximity to a horizontal plane (H) containing the axis of the intake path (2), a groove-shaped second passage (35b) formed between mating faces of the throttle body (1) and the sensor housing (17) so as to extend while bending upward from the other end of the first passage (35a) at substantially right angles, and a third passage (35c) formed in the throttle body (1) so as to extend from the upper end of the second passage (35b) in a direction opposite to the first passage (35a) and reach the negative

Abstract: An engine control module having an environmentally-sealed housing includes a housing-mounted air pressure sensor for providing a reliable measure of atmospheric air pressure to a control circuit mounted within the housing. The sensor is mounted on an inboard face of the housing, and includes a sensor element, a body portion and a riser portion. The sensor element is mounted in the body portion, and the riser portion protrudes through an opening in the housing to couple the sensor element to atmospheric pressure outside the housing. The body portion is sealingly secured to the inboard face of the housing, and a set of conductor pins molded into the body portion extend inward to engage a circuit board enclosed by the housing, and thereby directly couple the sensor element to the ECM's control circuit. The top of the riser portion is capped by a splash-proof lid to prevent water intrusion.

Abstract: A restriction diagnostic system for a vehicle comprises a pressure difference module and a diagnostic module. The pressure difference module determines a pressure difference between an ambient air pressure and a filtered air pressure measured at a location between an air filter and a valve that is selectively opened to enable ambient airflow through the air filter to a fuel vapor canister. The diagnostic module selectively diagnoses restriction of the airflow through the air filter when the pressure difference is greater than a predetermined pressure.