VR6 technical information (AAA)

Volkswagen of America, Inc.

Printed in U.S.A.
Printed 12/91
Part # WSP 521-402-00

All rights reserved. All information contained
in this manual is based on the latest product
information available at the time of printing.
The right is reserved to make changes at any
time without notice.

Always check Technical Bulletins and the mirofiche
system for information that may supersede any
information included in this manual.


*** Introduction ***

Volkswagen has developed a new six-cylinder engine called the VR-6.
This 2.8-liter engine is unique in that the V-angle between cylinder
banks is 15° rather than the 60° or 90° found in most conventional
V-6 engine designs.

The engine features a cast-iron crankcase, one light alloy crossflow
cylinder head with two valves per cylinder operated by chain-driven
overhead camshafts.

All fuel and ignition requirements of the VR-6 engine are controlled
by the Bosch Motronic M2.9 Engine Management System.

This Engine Management System features an air mass sensor, dual knock
sensors for cylinder-selective ignition knock regulation, and Lambda
regulation.

Exhaust gases are channeled through a 3-way catalytic converter.


*** Engine Specifications ***

Engine code: AAA
Design: Four-stroke, internal combustion engine in "Vee"/in-line
Displacement: 2.8 liter
Bore diameter: 81.0 mm
Stroke: 90.0 mm
"Vee" angle: 15°
Compression ratio: 10:1
Fuel and ignition systems: Bosch Motronic M2.9
Emission control: Lambda control with catalytic converter

The name, VR-6 come from a combination of Vee and the German word
Reihenmotor. The combination of the two can be roughly translated
as "in-line Vee."

Volkswagen has designed the 15° VR-6 to take advantage of
conventional in-line six-cylinder engine features (single cylinder
head, narrow width and excellent balancing) with the advantages
of a V-6 engine design (short overall length and compactness).

*** VR-6 ***

The VR-6 was specifically designed for transverse installation
in front-wheel-drive vehicles. By using the narrow 15° VR-6 engine,
it was possible to install a six-cylinder engine in existing
Volkswagen models.

*** V-6 Conventional Design ***

A wider V-6 engine of conventional design would have required
lengthening existing vehicles to provide enough crumple zone
between the front of the vehicle and the engine, and between
the engine and the passenger cell.

Using the narrow VR-6 engine will help Volkswagen meet current
and future front-end crash standards.

*** Overview ***

The drop-forged steel, six-throw crankshaft runs in seven main
bearings. The connecting rod journals are offset 22° to one
another.

Overhead camshafts (one for each bank of cylinders) operate the
hydraulic valve lifters which, in turn, open and close the 39.0-mm
intake valves and 34.3-mm exhaust valves.

Because of the special VR-6 cylinder arrangement with two rows
of combustion chambers in the same cylinder head, the intake
runners between the two cylinder banks are of varying lengths.

The difference in intake length is compensated in the overhead
intake manifold. Each runner is 420 mm long.

Exhaust gases are channeled from two 3-branch cat-iron exhaust
manifolds into a sheathed Y-pipe. From there, they are channeled
into a single flow before passing over the heated Oxygen Sensor
and then to the catalytic converter.

The oil pump driveshaft is driven by the intermediate shaft.

Fuel injectors of the Bosch M2.9 Engine Management System are
mounted behind the bend of the intake manifolds. Besides being
the optimum location for fuel injection, this location also helps
shield the injectors during a frontal impact.

The water pump housing is cast integral with the engine crankcase.
In addition to the belt-driven water pump, VR-6 engine will use
an auxiliary electric pump to circulate water while the engine is
running and during the cooling fan after-run cycle.

In the interest of environmental friendliness, a replaceable oil
filter cartridge is used on the VR-6 engine.

The sump-mounted oil pump is driven via the intermediate shaft.
An oil pressure control valve is integrated in the pump.

*** Crankcase ***

The crankcase is made from Perlitic gray cast iron with micro-alloy.
Two banks of three cylinders are arranged at a 15° axial angle from
the crankshaft.

The cylinder bores are 81 mm in diameter with a spacing of 65 mm
between cylinders. They are staggered along the length of the
engine block to allow the engine to be shorter and more compact
than conventional V-6 engines.

The centerline of the cylinders are also offset from the centerline
of the crankshaft by 12.5 mm.

To accommodate the offset cylinder placement and narrow "Vee"
design, the connecting rod journals are offset 22° to each other.
This also allows the use of a 120° firing interval between cylinders.
The firing order is: 1, 5, 3, 6, 2, 4

*** Cylinder Head ***

The aluminum crossflow cylinder head is manufactured in a permanent
mold casting. The combustion-chamber side of the head is hardened
through a separate chill casting

Twenty stretch bolts are used to retain the cylinder head to the block.
These bolts are accessible even with the camshafts installed.
However, it is necessary to retorque the bolts after installation.
Holes for bolts, numbers 12 and 20 are sleeved to make cylinder head
installation easier.

To help optimize flow through the cylinder head, the area above the
valve seats has been machined. Valve shaft diameter has been reduced
to 7.0 mm during development.

Cylinders 1, 3, and 5 have short intake runners and long exhaust
runners while cylinders 2, 4, and 6 have long intake runners and
short exhaust runners.

A crossflow cylinder head has allowed the use of a single cylinder
exhaust manifold rather than a manifold for each bank.

*** Combustion Chamber ***

The surface of the combustion side of the cylinder head is flat.
The combustion chamber is formed by the shape of the piston head.

Ten different piston designs were tested during development of the
VR-6 engine.

The result of these tests was the selection of a slanted piston
head within eccentric trough. The trough is offset from the center
of the piston by 4.0 mm.

Compression gap height (at TDC) is 1.5 mm. the compression ratio is
10:1.

*** Chain tensioners ***

Operated by oil pressure and spring tension.

The camshafts are driven by a two-stage chain-drive system located
on the flywheel side of the engine.

Chains were selected to drive the valve train in consideration of
a Diesel version of the VR-6 engine.

A single chain (lower) is driven by the crankshaft which, in turn,
drives an intermediate sprocket and shaft at a ratio of 3:4.

The intermediate shaft sprocket drives the camshafts via a double
roller chain (upper) at a ratio of 2:3. A double roller chain is
used to drive the camshaft sprockets because it must transfer more
torque than the lower chain.

The specific gear ratio selection was chosen in order to keep the
camshaft sprocket size small. This helps keep the overall engine
height to a minimum.

Chain tension is maintained by two chain tensioners. The upper
chain tensioner is hydraulically operated by engine oil pressure
and spring tension.

The lower chain tensioner (with mechanical lock) is operated by
spring tension and lubricated with engine oil.

Chain flutter is prevented by guide rails on the slack side of
both chains.

*** Engine Cooling System ***

The VR-6 Engine uses an impeller-type water pump driven by the
poly-ribbed belt.

The pump housing itself is cast into the engine block adjacent
to cylinder number 2.

In addition, an Auxiliary Electric Coolant Pump also circulates
engine coolant anytime the ignition is switched on.

The Auxiliary Electric Coolant Pump also runs when the engine
is switched off and the coolant temperature goes over 107° C (220° F).
It runs in conjunction with the Radiator Cooling After-run System.

Circulating the coolant during this time helps cool the engine
block and prevent the possibility of air pockets forming in the
cylinder head.

The thermostat housing of the cooling system also houses the
temperature senders G2, and F87 for the Radiator Cooling After-run
System, and temperature sender G62 for the Motronic Engine Management
System.

*** Intake Manifold ***

Volumetric efficiency must be uniform to attain smooth engine
running and optimal power output under all operating conditions.
This, in turn, requires identical flow conditions in the intake
ports of all cylinders.

Since the lengths of the intake runners in the VR-6 cylinder head
are not equal, it was necessary to compensate with the internal
design of the intake manifold.

All air intake passages are 420 mm long.

*** Auxiliary Drives ***

A double-sided poly-ribbed belt drives all the auxiliary components
of the VR-6 engine.

A spring-operated tensioning roller keeps the poly-ribbed belt at
the proper tension. The belt tension is released by threading a
long 8 mm bolt into a threaded hole on the tensioner.

*** System Overview ***

The VR-6 engine will use the Motronic Engine Management System
version M2.9.

All Corrados will have EGR while only California-version Passats
will have EGR.

*** Fuel Delivery System ***

A two stage fuel pump supplies fuel through the filter to the fuel
manifold and the four hole injectors. The pump is located in the
fuel tank.

The fuel manifold is located on the intake manifold. A fuel pressure
regulator is attached to the fuel manifold on the fuel return side.

The fuel pressure regulator is a diaphragm-type regulator. Fuel
pressure is regulated depending on intake manifold pressure.

As intake manifold pressure changes, the pressure regulator will
increase or decrease the system fuel pressure. This maintains
constant pressure differences between the intake manifold pressure
and fuel pressure.

*** Two-Stage Fuel Pump ***

The two-stage pump has one motor that drives two separate pumps.

* Stage One *

Fuel is drawn in through a screen at the bottom of the housing
by a vane-type pump. The vane-type pump acts as a transfer pump.
It's designed to supply fuel to the fuel accumulator which is
within the pump housing.

Fuel vapors and air bubbles from fuel returning from the engine,
as well as excessive fuel, is forced out of the accumulator through
a fuel vent.

* Stage Two *

The gear-type pump draws fuel in from the bottom of the accumulator
and through a screen. The fuel is then forced through the pump
housing by the gear pump and out the top.

*** Fuel Injectors ***

The injectors are supplied 12 volts by the Power Supply Relay and
are grounded through the Motronic ECU. They are opened sequentially
in the cylinder firing order.

Injection quantity is determined by the injector opening time.

*** Fuel Tank Ventilation ***

The following inputs are used to control the fuel tank ventilation:

.Engine speed
.Engine load
.Engine coolant temperature
.Signal from throttle valve Potentiometer (G69)

Fuel vapors from the fuel tank are vented to the carbon canister.
When the engine is warm and above idle speed, the vapors will be
drawn into the intake manifold via the carbon canister.

Depending on engine load and oxygen sensor signal, a frequency valve
will regulate the quantity of vapors entering the intake manifold from
the carbon canister

* Carbon Canister Frequency Valve (N80) *

The ECU determines the duty cycle of the frequency valve to regulate
the flow of fuel vapors from the carbon canister to the engine.

When no current is supplied to the valve, it remains in the open
position.
The valve is closed (duty cycle 100%) when the cold engine is started.

* Triggering: *

The Carbon Canister Frequency Valve (N80) begins to operate after
oxygen sensor operation has begun.

Valve operation is load- and speed-dependent during driving operation.
The valve is completely open at full throttle and completely closed
during deceleration fuel shut-off.

* Substitute function: *

If power to the valve is interrupted, the valve remains completely open.
This could lead to rough running at idle speed and during partial load
acceleration.

* Self-diagnosis: *

The ECU recognizes open circuits and short circuits in the component.

*** Air Mass Sensor (G70) ***

A hot-wire air mass sensor is used to measure the airflow into the
engine. The air mass sensor is attached to the air filter housing.
The sensor housing includes a baffle grid which reduces air turbulence
and pulses. The sensor has no moving parts.

A thin, electrically-heated , platinum hot-wire in the sensor is kept
180°C (356°F) above the air temperature measured by the thin-layer
platinum temperature sensor.

As airflow increases, the wires are cooled and the resistance of the
sensors changes. Current to the platinum hot-wire changes to maintain
the constant temperature difference.

The resulting current change is converted to a voltage signal and is
used by the Motronic ECU to calculate the volume of air taken in.

Dirt or other contamination on the platinum wire can cause inaccurate
output signals. Because of this, the platinum wire is heated to 1000° C
(1832° F) for a period of one second each time the engine is switched
off to burn off this dirt or contamination.

If a fault develops with the signal from the air mass sensor, the signal
from the throttle potentiometer is used as a substitute in order for
the car to remain derivable.

*** Throttle Valve Potentiometer (G69) ***

The throttle valve potentiometer is connected to the throttle valve
shaft. It informs the ECU about the power requested by the driver.

Idle and full load switched are not incorporated in the Throttle Valve
Potentiometer. Idle speed and full throttle applications are recognized
by the ECU from the voltage output of the potentiometer.

* Signal application: *

Throttle Valve Potentiometer signals are used for determination of idle
speed stabilization, idle air volume control, fuel after-run shut-off
and fuel load enrichment.

* Substitute function: *

The ECU uses the Air Mass Sensor signal and engine speed signal as a
replacement variables if the Throttle Valve Potentiometer fails.

* Self-diagnosis: *

Self-diagnosis recognizes:
Short circuits to positive
Short circuits to ground

Note: On vehicles with automatic transmission, this potentiometer is
combined in a housing with the potentiometer for the transmission
control.

*** Engine Speed / Reference Sensor (G28) ***

Engine speed and crankshaft position are registered by a single sensor
located on the engine block.

The sensor reads a toothed wheel mounted on the crankshaft to read
engine speed.

The toothed wheel has a two-tooth gap which is used as the measuring
point for the crankshaft position.

* Signal application: *

The signal is used for registration of engine speed and, in conjunction
with the signal from the Hall Sender, for recognition of ignition TDC
in cylinder Number 1.

* Substitute function: *

There is no substitute functions for Speed Reference Sensor G28.

* Self-diagnosis: *

The ECU recognizes a missing signal from the Speed/Reference Sensor
after cranking the engine for five seconds. An impaulsing signal
is recognizes by self-diagnosis when the reference mark signal and
Hall sender signal do not correspond.

* Hall Sender (G40) *

The Hall sender is mounted in the ignition distributor. It is an
electric control switch based on the Hall effect.

The hall sender consists of a magnetic enclosure and integrated
semiconductor circuit (the Hall IC). the IC is made of plastic to
protect it from dampness, soiling and mechanical damage.

A voltage signal is generated when the trigger wheel interrupts the
magnetic field created by the Hall IC. The trigger wheel turns at
camshaft speed. This means that the Hall sender generates one voltage
signal for every two crankshaft revolutions.

* Signal usage: *

The Hall Sender (G40) signal and the Engine Speed/Reference Sensor
(G28) signals are used to identify cylinder Number 1 for sequential
fuel injection and knock regulation.

* Substitute function: *

There is no substitute function for the Hall Sender signal. The
vehicle will start and run without this signal but the ignition
timing will be retarded and there will be no sequential fuel injection.

* Self-diagnosis: *

The ECU will recognize a break in wiring or a continuously applied
signal
voltage (during start attempts as well).

*** Knock Sensor I (G61) And Knock Sensor II (G66) ***

Two knock sensors are used. A knock sensor works like a microphone to
"listen" for spark knock or detonation.

When knocking occurs, the ignition timing is retarded until the knocking
is eliminated. Since the knock limit differs from cylinder to cylinder
and changes within the operating range, knock regulation is done
cylinder
selectively.

* Signal usage: *

Knock regulation does not occur until the engine coolant temperature of
40° C (104° F) is reached. Knock sensor I (G61) monitors cylinders 1,
2,
and 3. Knock sensor II (G66) monitors cylinder s 4, 5 and 6.

With the aid of the Hall sender signal, the ECU can determine which
cylinder is knocking. The ignition angle of the knocking cylinder is
retarded in steps until the knocking stops up to a maximum of 12°.

If spark knock is still detected, the ECU will retard the ignition
timing 11° for all cylinders and record a fault.

* Substitute function: *

If a knock sensor fails, the ignition timing angle of its assigned
cylinders is retarded.

* Self-diagnosis: *

The ECU recognized an open circuit if no signal from knock sensor I
(G61)
or knock sensor II (G66) is received by the ECU at an engine coolant
temperature above 40° C (104° F).

*** Oxygen Sensor (G39) ***

The oxygen sensor (G39) is made of a ceramic material called zirconium
dioxide. The inner and outer surfaces of the ceramic material are
coated with platinum. The outer platinum surface is exposed to the
exhaust gas, while the inner surface is exposed to the outside air.

The difference in the amount of oxygen contacting the inner and outer
surfaces of the oxygen sensor creates a pressure differential which
results in a small voltage signal in the range of 100 to 1000 mV.
The amount of voltage that is produced is determined by the fuel
mixture.

The oxygen sensor (G39) is heated electrically to keep it at constant
operating temperature. The heater also ensures that the sensor comes
to operating temperature quickly.

The sensor has four wires. Two are for the heating element (ground and
power). One wire is a signal wire for the sensor and one for the
ground.

* Signal usage: *

The base injection time is corrected according to the voltage signal
from the oxygen sensor to maintain a fuel/air ratio of approximately
14.7:1.
This allows the three-way catalytic converter to operate at its maximum
efficiency.

If the fuel mixture is lean (excess oxygen), the oxygen sensor will send
a low voltage signal (about 100mV) to the ECU.

If the fuel mixture is rich (lack of oxygen), the oxygen sensor will
send
a voltage signal (about 900 mV) to the ECU.

* Substitute function: *

There is no substitute function for oxygen sensor (G39). If signal
fails,
no oxygen sensor regulation takes place.

* Self-diagnosis: *

The ECU recognizes a fault if no reasonable signal voltage range is
attained within five minutes after engine start with an engine coolant
temperature over 40° C (104° F).

The ECU also recognizes a open circuit in the wiring or a short circuit
to ground andshort circuit to positive (sensor heating).

*** Coolant Temperature Sensor (G62) ***

Coolant Temperature Sensor (G62) is an NTC resistor. It's located in
the
thermostat housing. AS engine coolant temperature rises, the resistance
of the sensor goes down.

* Signal application: *

Coolant temperature sensor signals are required as a correction factor
for determination of ignition timing, injection timing and idle speed
stabilization.

In addition, these systems are activated depending on engine coolant
temperature:

.Knock control
.Adaptation of idle speed volume control
.Oxygen sensor operation
.Fuel tank venting

* Substitute function: *

A fixed value of 80° C (176° F) is stored in the memory of the ECU and
used in case of a faulty coolant temperature signal.

* Self-diagnosis: *

Self-diagnosis recognizes:

Short circuits to positive
Short circuits to ground

*** Intake Air Temperature Sensor (G42) ***

An intake air temperature sensor is located in the intake manifold on
the
left side.

* Signal application: *

The signal is used for idle stabilization and as a correction factor for
ignition timing.

* Substitute function: *

If a failure of the Intake Air Temperature Sensor (G42) occurs, the
Motronic Electronic Control Unit assumes a temperature of 20° C (68° F).
If this happens, cold start problems could occur at temperatures under
0° C (32° F).

* Self-diagnosis: *

The Motronic ECU recognizes open and short circuits to this component.

*** EGR System ***

All Corrados will come equipped with EGR (Exhaust Gas Recirculation).
Passats sold in California will be equipped with EGR. The EGR system is
used to reduce nitrous oxide emissions (Nox). The system recirculates a
small portion of exhaust gas into the intake mixture.

This exhaust gas is noncombustible and takes up a small space in the
intake charge. The results is lower combustion temperatures and reduced
Nox emissions.

The EGR system does not operate at idle because Nox emissions are low
during this time.

* EGR Frequency Valve (N18) *

The EGR Frequency Valve (N18) is mounted on the back of the intake
manifold. A control pressure (vacuum) is formed in the frequency valve
from the intake manifold pressure and atmospheric pressure (from the
intake air elbow). This pressure is applied to the EGR valve via the
EGR frequency valve (N18).

The frequency valve controls the amount of vacuum supplied to the EGR
valve by switching between the connection to the EGR valve and the
intake air boot.

Thus, the actual amount of recirculated exhaust gas can be determined
by the ECU, depending on engine speed and load conditions. A membrane
valve limits the vacuum supplied to the frequency valve at 200 mbar.

* Self-diagnosis: *

The ECU will recognize an open circuit or short circuit in the EGR
frequency valve. If the EGR valve remains continuously open or closed
because of mechanical failure, the EGR temperature sensor (G98) will
signal this to the control unit.

* Triggering: *

The frequency valve (N18) ground circuit is controlled by the ECU
depending on engine load and speed.

* Substitute function: *

There is no substitute function. If current to the frequency valve
(N18) is interrupted, the EGR valve will remain closed.

* EGR Temperature Sensor (G98) *

The EGR temperature sensor (G98) is located in the EGR valve exhaust
gas channel. It measures the temperature of the exhaust gas.

The sensor is an NTC resistor. The electrical resistance of the
sensor decreases as the temperature of the exhaust gas increases.

* Signal usage: *

The signal from the EGR temperature sensor (G98) is used only for
the diagnosis of the EGR system and has no influence on the control.

* Substitute function: *

There is no substitute function.

* Self-diagnosis: *

The EGR system is switched on when the engine coolant temperature
reaches 50° C (122° F).

*** Crankcase Ventilation ***

Crankcase vapors are vented from the cam cover to the intake air boot.

A heating element is used to prevent icing during cold weather.

PIN 1 = Positive (+)

PIN 2 - To engine ground

*** Idle Stabilizer Valve (N71) ***

* Triggering: *

The idle stabilizer valve (N71) is actuated on the ground side by the
ECU.

* Substitute function: *

When a defect in the circuit is recognized, both output stages are shut
off and the valve rotates to a fixed opening cross-section. This allows
the engine to idle at a warm engine idle speed.

* Self-diagnosis: *

The ECU recognizes open and short circuits in the component.

* Ignition System *

Input Signals for Regulation of Ignition System

.Engine speed
.Engine load
.Signal from knock sensors
.Signal from throttle valve potentiometer
.Coolant temperature
.Signal from Hall sender

Functions of Ignition System:

.Ignition timing correction
.Dwell angle regulation
.Idling speed stabilization
.Selective cylinder knock regulation

The control unit uses the engine load and engine speed signals as well
as
the signal from the throttle valve potentiometer to calculate the
ignition
timing.

If signals from the knock sensors indicate knocking combustion, the
control
unit retards the ignition timing of the knocking cylinder by 3° to max.
12°
until the knocking tendency of the concerned cylinder is reduced.

When the knocking tendency no longer exists, the ignition timing is
returned
to the nominal value in steps of 0.5°.

When knocking occurs, the ignition timing can be different for all
cylinders
because of the selective cylinder knock regulation.

Fluctuations in the idling speed range are compensated by changing the
ignition timing with the help of idling speed stabilization.

The control unit receives the idling speed signal from the throttle
valve
potentiometer.

Dwell angle regulation guarantees the necessary charging time of the
ignition coil and, therefore, ignition voltage, regardless of speed and
load conditions.

Coolant temperature signals are required to correct the ignition timing
of a cold engine and activate knock regulation.

*** Power Supply Components ***

Power for the Motronic Engine Management systems is supplied via Fuse
(S18) and three relays:

Fuel Pump Relay (J17)
(Position 12)

Power Supply Relay (J271)
(Position 3)

Oxygen Sensor Heater Power Supply Relay (J278)
(above main Central Electric Panel)

There is no internal power stage relay in the Motronic ECU.

Wiring for the Motronic Engine Management system is routed to the engine
via a single multi-pin connector. This makes engine removal quicker and
provides a test point for trouble shooting procedures.

A central ground station is located on the engine block below the intake
manifold.

It provides a ground point for:
.ECUs
.Sensors for the Motronic Engine Management system (and their shielding)
.Output components (injectors, etc.)



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