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The fuel injectors inject the fuel into the intake manifold manifold injec-tion or directly into the combustion cham-ber gasoline direct injection.. In the case of manifold injection, a

The function of the fuel-supply system is to deliver fuel at a defined pressure to the fuel injectors The fuel injectors inject the fuel into the intake manifold (manifold injec-tion) or directly into the combustion cham-ber (gasoline direct injection) In the case

of manifold injection, an electric fuel pump delivers the fuel from the tank to the fuel injectors In the case of gasoline direct in-jection, the fuel is likewise delivered from the tank by means of an electric fuel pump;

then it is compressed to a higher pressure

by a high-pressure pump and supplied to the high-pressure injectors

Fuel delivery with manifold injection

An electric fuel pump delivers the fuel and generates the injection pressure, which for manifold injection is typically about 0.3 0.4 MPa (3 4 bar) The built-up fuel pressure to a large extent prevents vapor bubbles from forming in the fuel system

A non-return valve integrated in the pump stops fuel from flowing back through the pump to the fuel tank and thereby main-tains the system pressure for a certain amount of time, even after the electric fuel pump has been switched off This prevents

the formation of vapor bubbles in the fuel system when the fuel heats up after the en-gine has been switched off

System with fuel return The fuel is drawn from the fuel tank (Fig 1, Pos 1) and passes through the fuel filter into

a high-pressure line, from where it flows to the engine-mounted fuel rail (7) The rail supplies the fuel to the fuel injectors (6) A mechanical pressure regulator (5) mounted

on the rail keeps the differential pressure be-tween the fuel injectors and the intake mani-fold constant, regardless of the absolute in-take-manifold pressure, i.e., the engine load The fuel not needed by the engine flows through the rail via a return line (8) con-nected to the pressure regulator back to the fuel tank The excess fuel heated in the engine compartment causes the fuel temper-ature in the tank to rise Fuel vapors are formed in the tank as a function of fuel tem-perature Ensuring adherence to environ-mental-protection regulations, the vapors are routed through a tank-ventilation system for intermediate storage in a carbon canister until they can be returned through the in-take manifold for combustion in the engine (evaporative-emissions control system) Fuel supply

Fig 1

1 Fuel tank

2 Electric fuel pump

3 Fuel filter

4 High-pressure line

5 Pressure regulator

6 Fuel injectors

7 Fuel rail

8 Return line

Fig 2

1 Suction-jet pump

for tank filling

2 Electric fuel pump

with fuel filter

3 Fuel-pressure

regulator

4 High-pressure line

5 Fuel rail

6 Fuel injectors

1 2

8

Fuel supply with manifold injection:

system with fuel return 1

4

6 5

3 2

1

Fuel supply with manifold injection:

returnless system 2

K Reif (Ed.), Gasoline Engine Management, Bosch Professional Automotive Information,

DOI 10.1007/978-3-658-03964-6_6, © Springer Fachmedien Wiesbaden 2015

Returnless system

In a returnless fuel-supply system (Fig 2),

the pressure regulator (3) is located in the

fuel tank or in its immediate vicinity A

re-turn line from the engine to the fuel tank is

therefore rendered superfluous

Since the pressure regulator on account

of its installation location has no reference

to the intake-manifold pressure, the relative

injection pressure here is not dependent on

the engine load This is taken into account

in the calculation of the injection duration

in the engine ECU

Only the amount of fuel which is to be

in-jected is delivered to the rail (5) The excess

flow volume delivered by the electric fuel

pump (2) returns directly to the fuel tank

without taking the circuitous route through

the engine compartment In this way, fuel

heating in the fuel tank and thus also

evapo-rative emissions are significantly lower than

in systems with fuel return

Because of these advantages, it is

return-less systems which are predominantly used

today

Demand-controlled system

In a demand-controlled system (Fig 3), the fuel-supply pump delivers only that amount

of fuel that is currently used by the engine and that is required to set up the desired pressure Pressure control is effected by means of a closed control loop in the engine ECU, whereby the current fuel pressure is recorded by a low-pressure sensor A me-chanical pressure regulator is rendered su-perfluous To adjust the delivery volume of the fuel-supply pump, its operating voltage

is altered by means of a clock module that is triggered by the engine ECU

The system is equipped with a pressure-relief valve (3) to prevent the buildup of excessive pressure even during overrun fuel cutoff or after the engine has been switched off

As a result of demand control, no excess fuel

is compressed and thus the capacity of the electric fuel pump minimized Compared with systems with maximum-delivery elec-tric fuel pumps, this lowers fuel consump-tion and can also reduce still further the fuel temperatures in the tank

Further advantages of a demand-con-trolled system are derived from the variably adjustable fuel pressure On the one hand, the pressure can be increased during hot starting to prevent the formation of vapor bubbles On the other hand, it is possible above all in turbocharging applications to extend the metering range of the fuel injec-tors by effecting a pressure increase at full load and a pressure decrease at very low loads

Furthermore, the measured fuel pressure provides for improved diagnostic options for the fuel system compared with previous systems In addition, the fact that the cur-rent fuel pressure is taken into account in the calculation of the injection duration results in higher-precision fuel metering

Fig 3

1 Suction-jet pump for tank filling

2 Electric fuel pump with fuel filter

3 Pressure-relief valve and pressure sensor

4 Clock module for controlling electric fuel pump

5 High-pressure line

6 Fuel rail

6 7 5

4

3

2

1

Fuel supply with manifold injection:

demand-controlled system

3

Fuel delivery with gasoline direct injection

Compared with injecting fuel into the intake manifold, there is only a limited time win-dow available for injecting fuel directly into the combustion chamber Increased impor-tance is also attached to mixture prepara-tion For this reason, fuel must be injected

at significantly higher pressure with direct injection than with manifold injection

The fuel system is divided into:

 Low-pressure circuit, and

 High-pressure circuit Low-pressure circuit Low-pressure circuits for gasoline direct in-jection essentially use the fuel systems and components known in manifold-injection systems Due to the fact that currently used high-pressure pumps require

increased predelivery pressure (admission pressure) in order

to prevent vapor-bubble for-mation during hot starts and high-temperature operation, it

is advantageous to use systems with variable low pressure

Demand-controlled low-pres-sure systems are particularly well suited here in that the optimum admission pressure

in each case can be set for every engine operating state

However, other systems are used They may be returnless systems with selectable admis-sion pressure (controlled by means of a shutoff valve) or systems featuring a constant, high admission pressure

High-pressure circuit The high-pressure circuit consists of

 High-pressure pump

 High-pressure fuel rail

 High-pressure sensor

and, depending on the system,

 Pressure-control valve, or

 Pressure-limiting valve Where both continuous-delivery and demand-controlled high-pressure systems are used in 1st-generation gasoline direct injection, 2nd-generation systems are demand-controlled

Depending on the operating point, a system pressure of between 5 and 12 MPa and in 2nd-generation systems of up to 20 MPa

is set by means of high-pressure control in the engine ECU The high-pressure injectors injecting the fuel directly into the engine’s combustion chamber are mounted on the fuel rail

Fig 1

1 1 Suction-jet pump

1 2 Electric fuel pump

with fuel filter

1 3 Pressure regulator

1 4 HDP1 high-pressure

pump

1 5 High-pressure

sensor

1 6 Fuel rail

1 7 Pressure-control

valve

1 8 High-pressure fuel

injectors

Fig 2

1 1 Suction-jet pump

1 2 Electric fuel pump

with fuel filter

1 3 Pressure-relief valve

and pressure sensor

1 4 Clock module for

controlling electric

fuel pump

1 5 Leakage line

(omit-ted from 2nd gen.)

1 6 HDP2 high-pressure

pump (2nd gen.:

HDP5)

1 7 High-pressure

sensor

1 8 Fuel rail

1 9 Pressure-limiting

valve (in 2nd gen.

integrated in

high-pressure pump)

10 High-pressure fuel

injectors

4

8

3 2 1

Fuel supply with gasoline direct injection (1st gen.):

continuous-delivery system 1

6

5

10

3 2 1

4

Fuel supply with gasoline direct injection (1st & 2nd gen.):

demand-controlled system 2

Continuous-delivery system

A high-pressure pump (Fig 1, Pos 4) driven

by the engine camshaft, normally a

three-barrel radial-piston pump, forces fuel into

the rail against the system pressure The

pump’s delivery quantity is not adjustable

The excess fuel not required for fuel

injec-tion or to maintain the pressure is

depres-surized by the pressure-control valve (7) and

returned to the low-pressure circuit For this

purpose, the pressure-control valve is

actu-ated by the engine ECU in such a way as to

obtain the injection pressure required at a

given operating point The pressure-control

valve doubles up as a mechanical

pressure-limiting valve

In continuous-delivery systems, most

of the operating points cause significantly

more fuel to be compressed to high system

pressure than is needed by the engine This

involves an unnecessary expenditure of

en-ergy and with it increased fuel consumption;

furthermore, the excess fuel depressurized

by the pressure-control valve contributes

to increasing the temperature in the fuel

system To avoid this problem,

controlled high-pressure systems are now

preferred

Demand-controlled system

In a demand-controlled system, the

high-pressure pump – usually a single-barrel

radial-piston pump – delivers to the fuel

rail only that amount of fuel which is

actu-ally needed for injection and to maintain the

pressure (Fig 2) The pump (6) is driven by

the engine camshaft The delivery quantity

is adjusted by a fuel-supply control valve:

The engine ECU actuates the pump’s

fuel-supply control valve in such a way as to

obtain in the rail the necessary system

pressure for a given operating point

For safety reasons, the high-pressure

cir-cuit features an integrated mechanical

pres-sure-limiting valve; this valve is mounted on

the fuel rail (8) in the case of 1st-generation

gasoline direct injection, and integrated

di-rectly in the high-pressure pump in the case

of the 2nd generation Should the pressure

exceed the permissible level, fuel is returned via the pressure-limiting valve to the low-pressure circuit

Evaporative-emissions control system

Vehicles with gasoline engines are equipped with an evaporative-emissions control sys-tem to prevent fuel that evaporates from the fuel tank from escaping to atmosphere

The maximum permissible limits for evapo-rative hydrocarbon emissions are laid down

in emission-control legislation

Design and method of operation Fuel vapor is routed via a vent line (Fig 3, Pos 2) from the fuel tank (1) to the carbon canister (3) The activated carbon absorbs the fuel contained in the fuel vapor and allows the air to escape to atmosphere through the fresh-air inlet opening (4)

In order to ensure that the carbon canister

is always able to absorb freshly evaporating fuel, the activated carbon must be regener-ated at regular intervals The carbon canister

is connected to the intake manifold (8) via

a canister-purge valve (5) for this purpose

Fig 3

1 Fuel tank

2 Fuel-tank vent line

3 Carbon canister

4 Fresh air

5 Canister-purge valve

6 Line to intake manifold

7 Throttle valve

1

6 6

8

5

4

2

Evaporative-emissions control system 3

To regenerate, the canister-purge valve is actuated by the engine-management system and opens the line connecting the canister

to the intake manifold Fresh air (4) is drawn

in through the activated carbon as a result of the vacuum pressure in the intake manifold

The fresh air takes up the absorbed fuel from the carbon canister and carries it to the intake manifold From there, it passes with the air inducted by the engine into the com-bustion chamber The injected fuel quantity

is simultaneously reduced so that the correct fuel quantity is available The fuel quantity drawn in through the carbon canister is cal-culated by means of the measured excess-air factor λ and regulated to a setpoint value

The purge-gas quantity, i.e the air/fuel mix-ture that flows in through the canister-purge valve, is limited due to possible fluctuations

of the fuel concentration; this is because the greater the proportion of fuel supplied through the valve, the quicker and more intensively the system will have to correct the injected fuel quantity This correction

is effected by means of lambda closed-loop control, whereby fluctuations of concentra-tion are necessarily compensated for with a time delay In order not to impair exhaust-gas values and driveability, it is essential for fluctuations of the lambda value to be kept

to a minimum by limiting the purge-gas quantity

Gasoline direction injection: special features The effect of purging is limited in systems with gasoline direct injection in stratified-charge mode since the extensive dethrottling gives rise to a low intake-manifold vacuum

This results in reduced purge-gas flow com-pared to homogeneous operation For in-stance, if the purge-gas flow is inadequate for coping with high levels of gasoline evaporation, the engine must be operated

in homogeneous mode until the high con-centrations of gasoline in the purge-gas flow have dropped far enough

Fuel-vapor generation Increased evaporation of fuel from the fuel tank is caused when

 The fuel in the fuel tank is heated up on account of increased ambient tempera-ture, by adjoining hot components (e.g., exhaust system) or by the return

of heated fuel to the fuel tank

 The ambient pressure drops, e.g when driving up a hill in mountain environ-ments

Electric fuel pump Function

The electric fuel pump must in all operating states deliver enough fuel to the engine at a high enough pressure to permit efficient fuel injection The most important performance demands made on the pump are:

 Delivery quantity between 60 and 250l/h

at nominal voltage

 Pressure in the fuel system between 300 and 650 kPa (3.0 6.5 bar)

 Buildup of system pressure from 50 60%

of nominal voltage; the decisive factor here is operation during cold starting Apart from this, the electric fuel pump is increasingly being used as the pre-supply pump for modern direct-injection systems used on both gasoline and diesel engines

In the case of gasoline direct injection, sometimes pressures of up to 700 kPa must

be provided during hot-delivery operation Design

The electric fuel pump comprises:

 Fitting cover (Fig 1, A) with electrical connections, non-return valve (preventing fuel from escaping from the fuel system) and hydraulic outlet The fitting cover usually also contains the carbon brushes for operating the commutator drive mo-tor and interference-suppression elements (inductance coils and, if necessary, capaci-tors)

 Electric motor (B) with armature and

per-manent magnet (a copper commutator is

standard, carbon commutators are used for

special applications and diesel systems)

 Pump section (C), designed as a

positive-displacement or flow-type pump

Types

Positive-displacement pump

In a positive-displacement pump, volumes

of liquid are basically drawn in and

trans-ported in a closed chamber (apart from

leaks) by rotation of the pump element to

the high-pressure side A roller-cell pump

(Fig 2a), an internal-gear pump (Fig 2b)

or a screw-spindle pump may be used for

the electric fuel pump

Positive-displacement pumps are

advanta-geous at high system pressures (450 kPa and

above) and have a good low-voltage

charac-teristic, i.e., they have a relatively “flat”

deliv-ery-rate characteristic over the operating

voltage Efficiency can be as high as 25 %

Pressure pulsations, which are unavoidable,

can cause audible noise depending on the

particular design details and installation

conditions

Whereas in electronic gasoline-injection systems the positive-displacement pump has to a large extent been superseded by the flow-type pump for the classical electric-fuel-pump requirements, it has gained a new field of application as the pre-supply pump

on direct-injection systems (gasoline and diesel) with their significantly greater pres-sure requirements and viscosity range

Fig 1

1 Electrical connection

2 Hydraulic connection (fuel outlet)

3 Non-return valve

4 Carbon brushes

5 Motor armature with permanent magnet

6 Flow-type-pump impeller

7 Hydraulic connection (fuel inlet)

Fig 2

a Roller-cell pump

b Internal-gear pump

c Peripheral pump

A Intake port

B Outlet

1 Slotted rotor (eccentric)

2 Roller

3 Inner drive wheel

4 Rotor

5 Impeller

6 Impeller blades

7 Passage (peripheral)

1

2

3

4

5

A

B

C 6

7

Design of an electric fuel pump –

example: flow-type pump

1

b

c

A

B

B A

B

A

A

A

3 4

2

Operating principles of electric fuel pumps 2

Flow-type pump The flow-type pump has become the ac-cepted solution for gasoline applications

up to 500 kPa An impeller with numerous blades (Fig 2c, Pos 6) around its periphery rotates in a chamber consisting of two fixed housing sections These housing sections feature a passage (7) in each case in the area

of the impeller blades These passages begin

at the height of the intake port (A) and end

at the point where the fuel exits the pump section at system pressure (B) For the pur-pose of improving the hot-delivery charac-teristics, a small degassing bore is provided

at a given angle and distance from the intake port, which (at the expense of a very slight internal leakage) facilitates the exit of any gas bubbles which may be in the fuel

Pressure builds up along the passage as

a result of the exchange of pulses between the impeller blades and the liquid particles

This leads to spiral-shaped rotation of the liquid volume trapped in the impeller and

in the passages

Flow-type pumps feature a low noise level since pressure buildup takes place con-tinuously and is practically pulsation-free

They are much simpler in terms of design and construction than positive-displace-ment pumps Single-stage pumps can gener-ate system pressures of up to 500 kPa

The efficiency of these pumps can be

as high as 22 %

Outlook Some modern vehicles are already supplied with fuel by demand-controlled fuel-supply systems In these systems, an electronic module drives the pump as a function of the required pressure, which is monitored

by a fuel-pressure sensor The advantages

of such systems are:

 Low current consumption

 Reduced heat entry through the electric motor

 Reduced pump noise, and

 Possibility of setting variable pressures in the fuel system

In future systems, pure pump control will

be extended to included further functions Examples include:

 Tank-leakage diagnosis and evaluation of the fuel-level-sensor signal

 Actuation of valves, e.g., for fuel-vapor management

In order to comply with the increasing de-mands with regard to pressure and service life and the differing fuel grades around the world, non-contact motors with electronic commutation will play a more important role in the future

Fuel-supply modules Whereas in the early stages of electronic gasoline injection the electric fuel pump was mounted exclusively outside the fuel tank (in-line), it is common practice today

to install the electric fuel pump inside the tank itself In this case, the electric fuel pump forms an integral part of a supply module which may comprise further elements:

Fig 3

1 Fuel filter

2 Electric fuel pump

3 Jet pump

controlled)

4 Fuel-pressure

regulator

5 Fuel-level sensor

4

5

6 3

2 1

Fuel-supply module 3

 A bowl as fuel reservoir for cornering

(usually actively filled by a suction-jet

pump or passively by a flap system,

switchover valve or similar)

 A fuel-level sensor

 A pressure regulator in returnless systems

(RLFS)

 A suction filter for protecting the pump

 A pressure-side fuel fine filter, which does

not need to be changed over the entire

service life of the vehicle

 Electrical and hydraulic connections

 Furthermore, tank-pressure sensors

(for tank-leakage diagnosis), fuel-pressure

sensors (for demand-controlled systems)

and valves can be integrated

Gasoline filter

The function of the gasoline filter is to

absorb and permanently accumulate dirt

particles from the fuel so as to protect the

fuel-injection system against wear caused

by particle erosion

Design

Fuel filters for gasoline engines are located

on the pressure side after the fuel-supply

pump In-tank filters are the preferred

choice in newer vehicles, i.e., the filter is

in-tegrated in the fuel tank In this case, it must

always be designed as a lifetime filter, which

does not need to be changed over the full

service life of the vehicle Furthermore,

in-line filters, which are installed in the fuel

line, continue to be used These can be

de-signed as replacement parts or lifetime parts

The filter housing is manufactured from

steel, aluminum or plastic It is connected to

the fuel feed line by a thread, tube or

quick-action connection The housing contains the

filter element, which filters the dirt particles

out of the fuel The filter element is

inte-grated in the fuel circuit in such a way that

fuel passes through the entire surface of the

filter medium as much as possible at the

same flow velocity

Filter medium Special resin-impregnated microfiber papers which are also bonded for higher-duty ap-plications to a synthetic-fiber (meltblown) layer are used as the filter medium This bond must ensure high mechanical, thermal and chemical stability The paper porosity and the pore distribution of the filter paper determine the filtration efficiency and throughflow resistance of the filter

Filters for gasoline engines are either spiral vee-form or radial vee-form in design In a spiral vee-form filter (Fig 1), an embossed filter paper is wrapped round a support tube The unfiltered fuel flows through the filter in the longitudinal direction

In a radial vee-form filter (Fig 2), the filter paper is folded and inserted into the hous-ing in the shape of a star Plastic, resin or metal end rings and, if necessary, an inner protective jacket provide stability The unfil-tered fuel flows through the filter from the outside inwards, during which the dirt parti-cles are separated from the filter medium

Fig 1

1 Fuel outlet

2 Filter cover

3 Support plate

4 Double flange

5 Support tube

6 Filter medium

7 Filter housing

8 Screw-on fitting

1

5

7

4

6

3

2

9

8

Gasoline filter with spiral vee-form element 1

Filtration effects Solid dirt particles are separated both by means of the straining effect and by means

of impact, diffusion and barrier effects

The straining effect is based on the fact that larger particles on account of their dimen-sions cannot pass through the filter’s pores

Smaller particles, on the other hand, adhere to filter-medium fibers when they strike these fibers Three different mecha-nisms are distinguished here: In the case of the barrier effect, the particles are flushed around the fibers with the fuel flow, but touch the edges of these fibers and are re-tained on these edges by intermolecular forces Heavier particles, because of their mass inertia, do not follow the fuel flow around the filter fibers; instead, they strike the fibers frontally (impact effect) In the case of the diffusion effect, very small parti-cles, on account of their proper motion (Brownian molecular motion), touch filter fibers by chance, at which point they adhere

to the fibers

The filtration efficiency of the individual effects is dependent on the size, the material and the rate of flow of the particles

Requirements The required filter fineness is dependent

on the fuel-injection system For manifold-injection systems, the filter element has a mean pore size of approximately 10 μm

Gasoline direct injection requires finer fil-tration The mean pore size is in the range

of 5 μm Particles which are more than 5 μm

in size must be separated at a rate of 85 %

In addition, a filter for gasoline direct injec-tion, when new, must satisfy the following residual-dirt requirement: Metal, mineral and plastic particles and glass fibers with diameters of more than 200 μm must be reliably filtered out of the fuel

Filter efficiency depends on the through-flow direction When replacing in-line fil-ters, it is imperative that the flow direction specified by the arrow be observed

The interval for changing conventional in-line filters is, depending on filter volume and fuel contamination, normally between 30,000 km and 90,000 km In-tank filters generally have change intervals of at least 160,000 km There are in-tank and in-line filters available for use with gasoline direct-injection systems which feature service lives

in excess of 250,000 km

Fig 2

1 Fuel outlet

2 Filter cover

3 Sealing ring

4 Internally welded

edge

5 Support ring

6 Filter medium

7 Filter housing

1

7

6

5

4

2

3

8

Gasoline filter with radial vee-form element 2

High-pressure pumps for

gasoline direct injection

Function

The function of the high-pressure pump

(German: Hochdruckpumpe, hence HDP) is

to compress a sufficient quantity of the fuel

delivered by the electric fuel pump at an

ad-mission pressure of 0.3 0.5 MPa (3 5 bar)

to the level required for high-pressure

injec-tion of 5 12 MPa (1st-generainjec-tion direct

injection) or 5 20 MPa (2nd-generation

direct injection)

Different high-pressure pumps are used in

the various direct-injection systems

Types

HDP1 (1st-generation direct injection,

continuous- delivery)

Design and method of operation

The HDP1 is a radial-piston pump with

three delivery barrels situated at

circumfer-ential offsets of 120° Figure 1 shows the lon-gitudinal and cross-sections of the HDP1

Driven by the engine camshaft, the drive shaft (13) rotates with the eccentric cam (1)

The eccentric cam converts the rotational motion via the cam ring (10) and the slipper (2) in a vertical motion of the pump pistons (4) The drive runs in gasoline for cooling and lubrication purposes

The fuel delivered by the electric fuel pump passes enters the HDP1 through the fuel inlet (9) The pump pistons contain transverse and longitudinal ports, through which the fuel enters the displacement chambers of the three delivery barrels

As the pump piston travels from top to bottom dead center, the fuel is drawn in through the inlet valve (7) In the delivery stroke, the drawn-in fuel is compressed as the pump piston travels from bottom to top dead center and delivered through the outlet valve into the high-pressure area

Fig 1

a Longitudinal section

b Cross-section

1 1 Eccentric cam

1 2 Slipper

1 3 Pump barrel

1 4 Pump piston (hollow piston, fuel inlet)

1 5 Sealing ball

1 6 Outlet valve

1 7 Inlet valve

1 8 High-pressure connection to fuel rail

1 9 Fuel inlet (low pressure)

10 Cam ring

11 Axial face seal

12 Static seal

1 10

4 3 7 6

2

1

8 5

9 10

2

3

4

11

13

7 6

12

HDP1 three-barrel pump

1