Self-Study Programme 210 EPC.pdf

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Service.
Self-Study Programme 210
Electronic Power Control
Design and Function
With the Electronic Power Control system, the
throttle valve is actuated only by an electric
motor.
This eliminates the need for a Bowden cable
between the accelerator pedal and the throttle
valve.
It means that the driver input is relayed to the
engine control unit via the accelerator pedal.
The engine control unit then sends a correspond-
ing command to the throttle valve positioner.
By positioning the throttle valve, the engine con-
trol unit can regulate engine torque even if the
driver has not depressed the accelerator pedal.
The result is better co-ordination between and
within the engine management systems.
We will now demonstrate that the Electronic Power Control is more than just a substitute for the Bowden
accelerator cable.
New
Important
Note
The Self-Study Programme
is not a Workshop Manual.
Please always refer to the relevant Service Literature
for all inspection, adjustment and repair instructions.
Service literature.
2
Table of contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Throttle valve positioning . . . . . . . . . . . . . . . . . . . . . . . . 4
System description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Control process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
System design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
What happens and when? . . . . . . . . . . . . . . . . . . . . . . 8
System components . . . . . . . . . . . . . . . . . . . . . . . . . . 10
System overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
The engine control unit . . . . . . . . . . . . . . . . . . . . . . . . . 11
The accelerator pedal module . . . . . . . . . . . . . . . . . . 14
The throttle valve control unit . . . . . . . . . . . . . . . . . . . 16
The fault indicator lamp . . . . . . . . . . . . . . . . . . . . . . . . 22
Auxiliary signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Function diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Self-diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Test your knowledge . . . . . . . . . . . . . . . . . . . . . . . . . 30
3
Introduction
Throttle valve positioning
210_008
210_007
Mechanical throttle valve positioning system
With this system, the driver depresses the accel-
erator pedal and thus positions the throttle valve
mechanically by means of a Bowden cable.
When the driver depresses the accelerator
pedal, the engine management system cannot
control the position of the throttle valve.
To regulate engine torque, the engine manage-
ment system must refer to other controlled
variables such as ignition timing and injection
timing.
Throttle valve positioning by an electric motor
drive is only possible in the idling speed range
and in combination with the Volkswagen cruise
control system.
Electric throttle valve positioning system
With this system, the throttle valve is positioned
by an electric motor across the full adjustment
range.
The driver depresses the accelerator pedal
according to the engine power required. Senders
register the accelerator pedal position and relay
this information to the engine control unit. The
engine control unit now sends a signal corre-
sponding to the driver input to the throttle valve
positioner which in turn sets the throttle valve to
the appropriate angle.
If the engine torque has to be adjusted for rea-
sons of safety or fuel consumption, however, the
engine control unit can adjust the position of the
throttle valve independent of the accelerator
pedal position.
The advantage of this is that the control unit
defines the position of the throttle valve
according to the various individual requirements
(driver input, exhaust emissions, fuel consump-
tion and safety).
4
System description
Internal
requirements
Engine
control unit
External
requirements
Optimal
efficiency
210_009
The "tools“ which the engine management system uses to influence the engine torque are:
throttle valve, charge pressure, injection timing, cylinder suppression and ignition advance angle.
Engine torque control with
mechanical throttle valve positioning
The various torque requirements are signalled
individually to the engine control unit and then
processed.
The torque demands cannot be matched opti-
mally because the engine control unit cannot
access the mechanically adjustable throttle valve
directly.
Engine torque control with
electric throttle valve positioning
This system permits torque-oriented
engine management.
What does this mean?
First, the engine control unit gathers all the
internal and external torque demands. Then it
calculates the necessary control actions.
This system is more precise and efficient than the
previous system.
Internal torque demands include:
-
-
-
-
-
-
Start
Catalytic converter heating
Idle speed control
Power limitation
Speed limiting device
Lambda control
External torque demands originate from:
- the automatic gearbox (shift point)
- the brake system (Traction Control System,
engine braking control)
- the air conditioning system
(air conditioner compressor ON/OFF) and
- the cruise control system
5

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