SYSTEM FUNCTIONS
The following system functions are described
- Power management
- Electronic immobilizer
- Comfort start
- Air supply: 2-stage differentiated air intake system "DISA"
- Charge monitoring
- "Valvetronic" variable valve gear
- "VANOS" variable camshaft control
- Fuel supply system
- Fuel injection
- Ignition-circuit monitoring
- Alternator actuation
- Oil supply
- Engine cooling
- Knock control
- Tank ventilation
- Lambda control system
- Torque monitoring
- Evaluation of road speed signal
- A/C compressor actuation
- Intelligent alternator regulation
- Active air flap control
Power management
The integrated supply module provides the power supply to the DME control unit.
3 relays in the integrated supply module distribute terminal 87 (power supply) to the various components.
For memory functions, the DME control unit also requires an uninterrupted power supply via terminal 30.
Terminal 30 also supplies power to the integrated supply module.
The earth connection for the DME control unit is provided by several pins which are connected inside the control unit.
Power management includes the following functions
- Closed-circuit current monitoring
- Consumer shutdown
- Control of the alternator
- Battery voltage monitoring
The battery voltage is regularly monitored by the DME control unit. If the battery voltage falls below approx. 6 volts or exceeds 24 volts, a fault is registered.
Diagnosis become active 3 minutes after the engine has started. This ensures that the effects of the starting operation or starting assistance on the battery voltage will not be registered as a fault.
- > E60, E61, E63, E64
The intelligent battery sensor (IBS) monitors the battery. The intelligent battery sensor is connected to the bit serial data interface (BSD).
- > E70
The fuse box supplies power to the DME control unit via the front power distributor in the junction box (for terminal 30 and terminal 87).
The intelligent battery sensor (IBS) monitors the battery.
Electronic immobilizer
The electronic immobilizer is an anti-theft and start-enabling device.
The CAS control unit controls the electronic immobilizer.
Each remote control unit has a transponder chip. The ignition lock is surrounded by a ring antenna.
Power is supplied from the CAS control unit to the transponder chip via this coil (remote control key does not require a battery).
The power supply and data transfer function is performed according to the transformer principle. For this, the remote control sends identification data to the CAS control unit.
If the identification data are correct, the CAS control unit activates the starter via a relay which is located in the control unit.
At the same time, the CAS control unit sends the DME control unit an encoded release signal (alternating code) to start the engine. The DME control unit only enables the start if a correct release signal has been received from the CAS control unit.
These operations may result in a slight delay in starting (up to half a second).
The following faults are stored in the DME control unit
- Missing or disturbed release signal from the EWS control unit
- Alternating code from the CAS control unit does not tally with the alternating code computed by the DME control unit.
If a fault is detected, the engine start is blocked.
Convenient-start system
The convenient-start system allows the engine to be started in a user-friendly manner as the starter motor automatically remains engaged until the engine is running.
When the START-STOP button is pressed, the CAS control unit first activates terminal 15. The relief relay for the ignition coils is activated.
When the START-STOP button is pressed, the CAS control unit checks that the brake pedal is depressed and the selector lever is in P or N.
The engine start process runs as follows
- First, the EWS is checked via the EWS data wire.
- If the data is correct, the DME enables the ignition and the fuel injection.
- The CAS control unit switches battery voltage to the DME control unit via terminal 50E. This gives the signal for the required engine start.
- The CAS control unit switches battery voltage to the starter motor via terminal 50L. The starter motor is switched on by the DME via the starter inhibitor relay. > E65, E66 and E70 The DME switches the starter motor on.
- The starter motor continues to turn until the CAS control unit receives the "engine running" signal from the DME through the data bus. The terminals 50 are then switched off by the CAS control unit. If the engine does not start, the terminals 50L and 50E will be switched off after a maximum of 20 seconds. The engine start is thus aborted.
Air supply: 2-stage differentiated air intake system "DISA"
The intake strokes of the pistons generate cyclic pressure waves in the inlet pipe.
These pressure waves travel along the inlet pipe and are reflected by the closed inlet valves.
A precise matching of the inlet pipe length with the valve response time produces the following effect
Shortly before the inlet valve is closed, a pressure maximum of the reflected air wave reaches the inlet valve. This has a supercharging effect which pumps a higher proportion of fresh air into the cylinder.
The differentiated air intake system also makes use of the inherent benefits of both short and long inlet pipes.
- The effect of short inlet pipes or inlet pipes with a large diameter is a high efficiency in the upper engine speed range (and also low torque in the medium engine speed range).
- Long inlet pipes or inlet pipes with a small diameter make high torque in the medium engine speed range possible.
A front intake pipe is installed upstream of each resonating pipe. When the sliding sleeves are closed, the combined effect of the front intake pipe and resonating pipe is similar to that of a long inlet pipe.
The pulsating air column inside it increases torque in the medium engine speed range considerably.
To increase performance in the higher engine speed range, the sliding sleeves are opened. This largely reduces the dynamics in the front intake pipes. The short resonating pipes which are now effective can make high performance figures in the upper engine speed range possible.
The DME control unit adjusts the sliding sleeves via the two DISA servomotors (12 volts) with integrated transmission. Each DISA servomotor has one output stage. The information as to whether a downwards or upwards gearshift was made is saved by the DME control unit.
When the value falls below 4700 RPM, the DME control unit closes the sliding sleeve with the assistance of the DISA servomotors. When the value of 4800 RPM is exceeded, the sliding sleeves are opened again (N62B40TU: 4800 and 4900 RPM). At changeover, these engine speeds are displaced reciprocally (hysteresis) to prevent the sleeves opening and closing in rapid succession.
In the event of system failure, the sliding sleeves remain in their respective positions. The driver will be aware of system failure through a loss of power and reduction in the final speed.
Once the engine has been switched off (terminal 15 OFF), the sliding sleeves are run once to their limit position.
This prevents deposits accumulating and blockage of the sliding sleeve during longer journeys at low engine speeds.
Charge monitoring
The following input variables are used to monitor the charge state of the DME
- Throttle-valve angle
- Valvetronic lift
- Air intake pressure
- Intake air-mass
From these 4 input variables on the inlet side, the DME calculates the charge state for all operating conditions.
"Valvetronic" variable valve gear
Valvetronic was developed to reduce fuel consumption.
The quantity of air supplied to the engine when Valvetronic is active is adjusted by the variable valve lift on the inlet valve and not the throttle-valve actuator.
An electrically-adjustable eccentric shaft changes the action of the camshaft on the roller cam follower via an intermediate lever. The result of this is variable valve lift.
With Valvetronic, the throttle-valve actuator is activated for the following functions
- Engine start (warm-up)
- Idle speed control
- Full load operation
- Emergency operation
In all other operating conditions, the throttle valve only remains open far enough to induce a slight low pressure.
This low pressure is required to ventilate the tank, for example.
The DME control unit calculates the associated setting of Valvetronic using the position of the accelerator pedal and other variables.
The DME control unit activates the Valvetronic actuator motor on the cylinder head via the Valvetronic control unit. The Valvetronic actuator uses a worm gear to drive the eccentric shaft in the cylinder head oil chamber.
The eccentric shaft sensor records the current position of the eccentric shaft. The eccentric shaft sensor is equipped with 2 angle sensors.
The Valvetronic control unit adjusts the current position of the eccentric shaft via the Valvetronic actuator until the nominal position is reached.
For safety reasons, 2 angle sensors are used with characteristic curves which have opposing directions. Both signals are digitally transmitted to the DME control unit. The DME control unit supplies 5 volts to both angle sensors.
Both signals from the eccentric shaft sensors are continuously monitored by the DME control unit.
Checks are made as to whether the signals are plausible in their own right and also in relation to one another. The signals may not differ. Where a short circuit or fault develops, the signals lie outside the measuring range.
The DME control unit continuously checks whether the actual position of the eccentric shaft corresponds with its nominal position. This makes it possible to detect any stiff movements in the mechanics.
In the event of a fault, the valves are opened as wide as possible. The air supply is controlled by the throttle valve.
If the actual position of the eccentric shaft cannot be detected, the valves are opened to the maximum extent without regulation (controlled emergency operation).
In order to achieve the correct valve opening, an adaptation must be made to balance all tolerances in the valve gear. During this adaptation process, the mechanical stops on the eccentric shaft are adjusted.
The positions registered are subsequently saved. These positions are used as the basis for calculating the actual valve lift at any point during operation.
The adaptation process is automatic: Each time the engine is restarted, the position of the eccentric shaft is compared with the values registered. If following a repair, for example, a different position of the eccentric shaft is detected, the adaptation process is carried out. In addition, the adaptation can be initiated via the BMW diagnosis system.
"VANOS" variable camshaft control
The variable camshaft control improves torque in the low and medium engine speed range.
Due to a larger valve overlap, the volume of residual fumes at idle speed is reduced. A recirculation of internal exhaust gas in the part-load range reduces the volume of nitrogen oxide.
The following is also achieved
- Faster heating of catalytic converters
- Reduced exhaust emissions following a cold start
- Reduced fuel consumption
A controlled VANOS adjustment unit is mounted at both intake and exhaust camshafts (controlled using oil pressure).
A VANOS solenoid valve is used to control the VANOS adjustment unit. The required position of the intake and exhaust camshaft is calculated using the engine speed and load signal (dependent on intake temperature and engine temperature). The DME control unit activates the VANOS adjustment unit accordingly.
The control of the intake and exhaust camshaft is variable within their maximum adjustment range.
Once the correct camshaft position has been reached, the VANOS solenoid valves ensure that the oil volume in the servo control cylinders in both chambers remains constant. This keeps the camshafts in this position.
To perform the adjustment, the variable camshaft control requires information on the current position of the camshaft. Camshaft sensors on the intake and exhaust end record the position of the camshafts.
When the engine is started, the inlet camshaft is in the end position ("retarded" position). When the engine is started, the exhaust camshaft is pretensioned by a spring and held in the "advanced" position.
Fuel supply system
- > E65, E66
The fuel supply system on the BMW 7-Series is requirement-orientated and thus depends on consumption.
The DME calculates the amount of fuel required on the basis of various operating variables.
In turn, the engine's current fuel requirement is calculated from this value. The DME requests this value as a volumetric flow with the unit "liters per hour".
The DME sends this request on the following path: DME (digital engine electronics -> PT-CAN -> SGM (safety and gateway module) -> byteflight -> SBSR (B-pillar satellite, right) -> EKP (regulated fuel pump).
The B-pillar satellite, right converts the amount of fuel requested into a nominal speed for the fuel pump.
The pump speed is regulated via the cycle ratio of a pulse-width-modulated signal. This rectangular signal gives the effective supply voltage for the fuel pump: The longer the pause between the edges of the rectangular signal, the lower the supply voltage for the fuel pump. The fuel pump delivery volume is correspondingly lower. The fuel pump speed is sent back to the B-pillar satellite, right as an input variable.
This method has the following benefits compared to the conventional way of actuating the fuel pump (fuel-pump relay)
- Lower current draw from fuel pump
- Reduced heating up of fuel
- Longer service life for fuel pump
- No fuel-pump relay needed
The flow of fuel is interrupted in the event of a crash of sufficient impact. This prevents the fuel from escaping or igniting (emergency fuel cutoff).
The fuel pump can be reactivated by switching the ignition off and on again.
If the request signal from the DME or the pulse-width-modulated signal from the SBSR is not received: The fuel pump will operate a maximum delivery capacity. This guarantees sufficient fuel supply for all operating conditions (emergency operation).
- > E60, E61, E63, E64 and E70
The DME switches the fuel pump on using the fuel-pump relay.
Fuel injection
During fully sequential fuel injection, each injector is controlled by means of its own final stage.
Fully sequential fuel injection has the following advantages
- Improved fuel preparation for each individual cylinder
- Adaptation of the fuel injection timing to suit the engine's operating condition (engine speed, load, engine temperature)
- Cylinder-selective correction of injected fuel quantity for varying load (during a cycle, the fuel injection timing can be corrected by extending or shortening it)
- Cylinder-selective cutoff (e.g. when an ignition coil is defective)
- Diagnosis for each individual injector possible
The control of each injector by means of its own individual final stage achieves a fuel build-up which is the same in all cylinders. This ensures a uniformly-effective fuel preparation throughout.
The fuel build-up time is variable and depends on the load, engine speed and engine temperature.
As it is only injected once per camshaft rotation, the spread of fuel due to tolerances in the components is reduced.
In addition, the idle-running performance is improved as the response and dropout times at the injectors are reduced.
Moreover, a marginal reduction in fuel consumption is also achieved.
When the vehicle is in motion and there is a sudden acceleration or the throttle is closed, the fuel injection period can be adjusted. If the injectors are still open, the mixture at every valve can be adjusted by extending or shortening the fuel injection period. This achieves an improved engine response.
Ignition-circuit monitoring
The current in the primary coil for the ignition coil is used to monitor the ignition circuit. When the engine is switched on, the current must stay within specific values during certain time thresholds.
The ignition diagnosis monitors the
- Primary power circuit for the ignition coil
- Ignition wiring harness
- Secondary power circuit for the ignition coil with the spark plug
The ignition-circuit monitoring can detect the following faults
- Short circuit at the primary end of the ignition coil
- Short circuit at the secondary end of the ignition coil
- Defective spark plug
- Break in wire to actuator
- Defective ignition output stage
The following are not detected
- Intermittent faults such as loose contacts in the wire to the actuator
- Spark-over in high-tension circuit parallel to spark gab where a short-circuit in the coil does not develop
Alternator actuation (bit-serial data interface)
The following functions have been implemented in the DME control unit for the alternator with bit-serial data interface (BSD)
- Switching the alternator on and off using defined parameters
- Specification of the alternator's maximum permissible power consumption
- Calculation of the input torque for the alternator based on the power consumption
- Control of the alternator's response when higher electrical loads are connected (load-response function)
- Diagnosis for the data line between the alternator and DME control unit
- Storage of faults which develop in the alternator in the fault memory of the DME control unit
- Actuation of the charge-current indicator light in the instrument cluster via bus connection
- Introduction of intelligent alternator regulation: > from 03/2007 in the E60, E61 > from 09/2007 in the E63, E64, E70
The principal function of the alternator is also guaranteed when communication between the alternator and DME control unit is interrupted.
The following fault causes can be distinguished in fault memory entries
- Overheating protection: The alternator is overloaded. For safety reasons, the alternator voltage is reduced until the alternator has cooled down (charge telltale light does not light up).
- Mechanical fault: There is a mechanical block in the alternator. or: The belt drive is defective.
- Electrical fault: Excitation diode defective, excitation coil has been interrupted, overvoltage due to defective governor.
- Communication failure: Line between DME control unit and alternator defective.
An interruption or short circuit in the alternator coils will not be detected.
Oil supply
The oil condition sensor reports the engine oil level and engine oil quality back to the DME control unit. A temperature sensor in the oil condition sensor indicates the engine oil temperature. The engine oil temperature is used together with the coolant temperature to calculate the engine temperature.
The oil pressure is indicated by the oil-pressure switch.
The oil level is also measured for the electronic oil level check. The 2nd capacitor in the upper part of the oil condition sensor registers the oil level. The capacitor is at the same level as the oil level in the oil sump.
As the oil level falls, the capacitance of the capacitor falls. The electronic evaluation unit creates a digital signal from this. The DME then calculates the engine oil level.
The DME control unit activates the warning and indicator lamp in the instrument cluster via the PT-CAN (red: oil pressure low; yellow: oil level low).
Electronic oil level check
The dipstick now has a black handle. The engine oil level is measured by the oil condition sensor.
The measured value is displayed in the Central Information Display (CID).
The signal from the oil condition sensor is evaluated in the DME. Besides the oil level, the thermal oil level sensor also indicates the engine oil temperature.
Condition Based Service
In addition, the engine oil quality is measured for the Condition Based Service (CBS).
The electrical material properties of the engine oil change as the engine oil wears and ages. The changed electrical properties of the engine oil (dielectrics) cause the capacity of the capacitor in the oil condition sensor to change.
The electronic evaluation unit converts the measured capacity into a digital signal.
The digital sensor signal is transmitted to the DME as a statement about the condition of the engine oil.
The DME uses this to calculate the next engine oil change as part of Condition Based Service (CBS).
Engine cooling
The opening and closing of the mapped thermostat is controlled by a characteristic map. This regulating operation can be split into 3 operating ranges
- Mapped thermostat closed: The coolant only flows through the engine and the coolant circuit is closed.
- Mapped thermostat open: The entire coolant volume flows through the radiator. This results in maximum use of the available cooling output.
- Control range of the mapped thermostat: A proportion of the coolant flows through the radiator. The mapped thermostat maintains a constant coolant temperature within the control range at the engine inlet. In this operating range, the coolant temperature can now be selectively controlled with the assistance of the mapped thermostat. This means that a high coolant temperature can be set in the part-load range of the engine. High operating temperatures in the part-load range result in improved combustion. This in turn leads to reduced consumption and exhaust emissions. During full load operation, certain disadvantages are associated with higher operating temperatures (retarding of ignition due to knock). A lower coolant temperature is therefore specifically set during full load operation with the assistance of the mapped thermostat.
Knock control
The engine is equipped with a cylinder-selective adaptive knock control.
4 knock sensors detect combustion knock (cylinders 1 and 2, cylinders 3 and 4, cylinders 5 and 6, cylinders 7 and 8). The sensor signals are evaluated in the DME control unit.
If the engine is operated with combustion knock for longer periods of time, this can cause serious damage.
Knock is encouraged by
- Increased compression ratio
- High cylinder fill levels
- Inferior fuel grade (RM/MM)
- High intake-air and engine temperature
The value of the compression ratio can also become too high due to spread due to deposits or the manufacturing process. On engines without knock control, these unfavorable influences must be taken into account. The design of the ignition system must include a safety gap to the anti-knock limit. This makes reduced efficiency in the upper load range unavoidable.
The knock control prevents knock. The firing point of the relevant cylinder (cylinder-selective) is set as far as possible in the retarded direction only when a knocking risk is present.
This means that the ignition control grid can be designed around ideal consumption values (without having to take the anti-knock limit into account). A safety margin is no longer necessary.
The knock control performs all the necessary corrections to the firing point due to knock and also makes trouble free driving with regular grade petrol (minimum RM 91) possible. The knock control provides
- Protection from damage caused by knock (also in unfavorable conditions)
- Reduced consumption and increased torque throughout the entire upper load range (according to the quality of fuel used)
- High economic efficiency through optimum use of the available fuel quality and by taking the specific engine condition into account
The knock control self-diagnosis performs the following checks
- Check for signal interference, e.g. breaks in wiring or defective connector
- Self-test for evaluating circuit
- Check of engine noise level recorded by the knock sensor
If a fault is identified during one of these checks, knock control is deactivated. An emergency program assumes control of the ignition angle. A fault is simultaneously registered in the fault memory. The emergency program guarantees damage-free operation from a minimum of RON 91. The emergency program depends on the load, engine speed and engine temperature.
Tank ventilation
The fuel evaporation control valve controls the regeneration of the activated carbon filter with scavenging air.
Scavenging air drawn through the activated carbon filter is enriched with hydrocarbons (HC) depending on the loading of the activated carbon. The scavenging air is subsequently fed to the engine for combustion.
The formation of hydrocarbons in the fuel tank is dependent on
- Fuel temperature and ambient temperature
- Air pressure
- Fill level in the fuel tank
In a current-free state, the fuel evaporation control valve is closed. This prevents the ingress of fuel vapor from the activated carbon filter into the inlet pipe when the engine is switched off.
Closed-loop Lambda control system
Optimum efficiency of the catalytic converter can only be achieved if an ideal fuel/air ratio is used for combustion. Oxygen sensors are used upstream and downstream of the catalytic converter.
The oxygen sensors upstream of the catalytic converter have a steady characteristic output curve (measure oxygen content in rich and lean ranges.)
The measurement method employed by this oxygen sensor is different to an oxygen sensor with an erratic characteristic output curve. The oxygen sensor is therefore connected using 6 pins instead of 4.
- Oxygen sensors upstream of catalytic converter The oxygen sensors upstream of the catalytic converter (control sensors) are used to assess the composition of the exhaust gas. The control sensors are screwed into the exhaust manifold. The oxygen sensors measure the residual oxygen content in the exhaust fumes. The voltage values determined are relayed to the DME control unit. The DME control unit corrects the mixture composition by adjusting the injection period. Values which are greater or less than l = 1 are aimed at depending on the operating condition.
- Oxygen sensors downstream of catalytic converter The oxygen sensors downstream of the catalytic converter (monitoring sensors) are used to monitor the control sensors. In addition to this, the function of the catalytic converter is monitored.
To ensure full operational reliability of the oxygen sensors upstream of the catalytic converter, a temperature of approximately 750 °C is required (350 °C for oxygen sensors downstream of the catalytic converter). For this reason, all oxygen sensors are heated.
The oxygen sensor heating is controlled by the DME control unit. When the engine is cold, the oxygen sensor heating remains switched off, as condensation which is present would otherwise destroy a hot oxygen sensor due to thermal strain.
This means that the closed-loop Lambda control only becomes active a short time after the engine has started, once the catalytic converters have warmed up. The oxygen sensor is initially warmed up using a reduced heating power, to avoid imposing unnecessary loads on it due to thermal strain.
Evaluation of road speed signal
The road speed signal is required by the DME control unit in order to perform several functions
- Speed limiting function: Once the maximum road speed has been reached, the fuel injection and ignition are adjusted. If required, individual ignition and injection signals are suppressed. A "soft" speed limiting function is thus carried out.
- Control of A/C compressor: When the air-conditioning system is switched on, the A/C compressor is switched off during full-load acceleration, provided that: the car's road speed is less than 13 km/h.
- Idle speed control: If the car's road speed is 0 km/h, the idle speed is adjusted (depends on A/C compressor ON, selected drive position for automatic transmission, light ON).
- Poor-road-surface detection: At low road speeds, the check for smooth engine operation is switched off.
A/C compressor activation
The DME control unit supplies the signal to actuate the A/C compressor.
The A/C compressor is switched off under the following conditions
- Full engine load
- car's road speed under 13 km/h
- Engine overheating
The IHKA actuates the A/C compressor. The DME sends the signal on the bus system.
Intelligent alternator regulation
Intelligent alternator regulation systematically controls the battery charge state.
The battery is predominantly charged in overrun mode.
Depending on the battery charge state, the battery will not be charged during an acceleration phase.
Active air flap control
Active air flap control regulates the air supply for the engine and assemblies cooling system by only opening the air flaps as they are needed.
The system functions of the vacuum system are described using the following examples
- Power assist for brakes
- Actuation of exhaust flaps
- Adjustment of variable turbine geometry
- Actuation of controlled damping mounts
- Exhaust gas recirculation
- Drawing off of blow-by gases from crankcase
- Blowing out activated charcoal filter
Power assist for brakes
The brake booster amplifies the force excerpted at the brake pedal. To do this, the brake booster stores part of the vacuum generated by the engine. The vacuum then amplifies the force generated by pressure on the brake pedal.
Actuation of exhaust flap
A controlled electropneumatic exhaust flap is fitted in the exhaust system. The exhaust flap enhances active sound-damping. The exhaust flap is closed by vacuum.
Actuation of controlled damping mounts
In the basic setting, there is no vacuum at the control component on the mount. The bypass in the mount is closed. Hydraulic fluid flows back and forth through a ring channel between the upper and lower chambers in the mount. The mount acts like a conventional hydraulic bearing. The mount has hard damping.
If a vacuum is applied to the mount's control component, the bypass will open. The hydraulic fluid then flows back and forth between the chambers through a larger cross-sectional area. The mount has softer damping.
Exhaust gas recirculation
With exhaust gas recirculation, part of the exhaust gas is take from behind the exhaust manifold. This is then fed back into the engine through the intake air duct. The exhaust gas recirculation pipe is located at the inlet to the intake manifold.
If a vacuum is applied to the exhaust gas recirculation valve, the exhaust gas recirculation pipe will open. The level of vacuum is determined by the opening in the exhaust gas recirculation valve.
Exhaust gases flow through a connecting pipe to the exhaust manifold and into the intake manifold.
Drawing off of blow-by gases from crankcase
The crankcase ventilation system uses vacuum to bleed the blow-by gases out of the engine block.
Blow-by gases are the small portion of the cylinder fill that passes by the piston rings and into the crankcase during compression. If the blow-by gases are not bled from the engine block through the crankcase ventilation system, they will accumulate in the crankcase. The blow-by gases would then apply pressure on the pistons from below. This would have a negative effect on the downward movement of the pistons in the intake stroke and operating stroke.
Blowing out activated charcoal filter
The fuel tank vent hose is connected to an activated charcoal filter. Vapors from the fuel tank are collected in the activated charcoal filter. The activated charcoal filter is connected to the intake manifold by a pipe. A fuel evaporation control valve is fitted in this pipe. When the fuel evaporation control valve is opened, the vacuum in the manifold draws in fresh air. At the same time, the fresh air blows out the fuel vapors collected in the activated charcoal filter.